Stage Set
In order to understand the current morass, it helps to know the field on which the coming elections will be fought.
First, Catalonia has a parliamentary system, competition in which dictates control of the Generalitat, the Catalan regional government. Restored in the waning years of the transition to democracy, the present Generalitat is a restoration of the regional government
which existed in the 1930s, and prior to the 18th century. Beginning with the Basque Country, Catalonia, and Galicia, Madrid devolved powers to the historic regions.
In the early 1980s, this was extended to the entirety of the country, creating regional governments known as autonomous communities in a process colloquially known as cafe para todos, coffee for all.

The Catalan regional assembly consists of 135 members elected via PR list from each of the four Catalan provinces. The largest province, centered on the capital Barcelona, elects 85 members, while the remainder are spread, more or less equally, among the other provinces. Building a stable governing coalition requires the support of 68 members. Up until the late 1990s, CiU could reliably depend on seat returns granting them an absolute majority. Beginning in the 1999 election, ERC began to eat into support for CiU, leading them to depend on the support of the main Spanish conservative party, PP. After an interlude in the period between 2003-2010 in which PSC, the local branch of PSOE, the Spanish socialists, ruled, CiU returned to power. Relying upon the abstention of PSC in order to install their leader as regional premier in 2010, subsequent snap elections, called in the wake of large demonstrations favoring Catalan independence, saw them first into an awkward coalition with rival ERC after the 2012 election. It is this government that ERC is threatening to bring down absent a genuine independence referendum, which, after all, had been a condition of their support for allowing CiU to take power in 2012.
Dramatis Personae
In the coming Catalan regional elections, 7-8 parties can, more or less, be depended upon to take seats in the new parliament. Briefly, these are:
CiU: Convergence and Union
Actually a coalition of two parties, similar to the relationship between the CDU and CSU in Germany, albeit without a territorial divide. The CDC, aka Convergence, is the larger of the two, and is further to the left both in terms of social/economic questions, in which it is essentially of Third Way. And in terms of Catalan nationalism, where it supports greater regional autonomy, but not independence. UDC, aka Union, is a Christian Democratic party that holds similar views on the nationalism issue, albeit more reticent about working with ERC. Traditionally the Catalan party of government, CiU has been in electoral union since 1978. Recent rumblings suggest that the more that Mas, the leader of CDC (and CiU), appeases ERC, the more likely UDC is to bolt. Until recently CiU could be depended upon to take between 30-60% of seats in the regional parliament. Current polling suggests that will fall to under 20% in the next election, further if Convergence and Union split.
PSC: Socialist Party of Catalonia
PSC is the Catalan branch of PSOE, the Spanish Socialists. Traditionally the second largest party in the Catalan assembly, PSC benefits enormously from CiU occupying the center right space usually held by the PP in the rest of Spain. From 2003-2010, PSC controlled the regional government with the support of two smaller left parties, including ERC. At times, the relationship between PSC and PSOE has been strained by the former's flirtations with federalism.
ERC: Republican Left of Catalonia
ERC occupies much of the left wing of the nationalist political space, and has been successful in recent years in drawing support away from CiU. Since the collapse of CiU dominance in the 1990s, ERC has been able to use its position as kingmaker in order to expand its representation in the regional assembly. It has been the primary beneficiary of the recent uptick in nationalist sentiment in the region, and it has been successful in channeling discontent with the politics of austerity coming from Madrid into support for Catalan nationalism. If successful in fracturing open CiU, ERC stands to assume the mantle of leadership on the nationalism issue away from them. ERC has significant, militant, internal tendencies, welcoming former members of Terra Lliure, a Catalan separatist organization, into its fold after they renounced armed struggle in the late 1980s. In their ease with militancy, ERC shares certain characteristics with Batasuna, and in fact prompted a major scandal for their PSC coalition partners when ERC leader Carod Rovira was found to have held a secret meeting with ETA members in France. Support for armed resistance has largely evaporated in the Basque Country, but there seems to be a growing appetite for militant action in certain quarters of the ERC.
PPC: Popular Party of Catalonia
PPC is the Catalan affiliate of the PP, the Spanish Conservatives. It has never been able to compete effectively in Catalan elections, however it did provide the necessary support for CiU to enter government in 1999, when it fell short of an absolute majority. PPC has much less independence than the PSOE branch, PSC, in the region. Almost always at the margin of Catalan politics, PPC only matters in tight situations, and in the coming elections it stands to lose seats to C's, Ciutadans, banishing it to total irrelevance. This trend to extinction in the region has not been lost on the national party, and seems to underlie the particularly hard line they take on the nationalism issue. This is somewhat ironic as CiU supported the PP in electing a PM during the Aznar years.
ICV: Initiative for Catalonia Greens
ICV is the local branch of IU, the Spanish United Left, and a collection of green groups. Stands at the margins, normally returning 5-10 seats in elections. A modest increase in support in recent years has waned as Podemos has emerged. ICV has been supportive of an independence referendum, and will tend to support ERC on these matters.
C's: Citizens
C's has emerged in recent years as a response to growing Catalan nationalism. Nominally a party of the center left in opposition to nationalism, the party draws support from, and flirts with, the far right. Think UKIP. Pulls support from PPC and the right wing of CiU. Will probably return 15-20 seats in the coming elections.
CUP: Popular Unity Candidates
CUP is a small left wing Catalan natonalist party. Largely supportive of the ERC take on the nationalism issue, although it is much further to the left on economic issues. First ran for the regional assembly in 2012. Will probably return 5-7 seats.
Podemos
Podemos hardly needs an introduction. After achieving a modest success in 2014 EP elections, support for the group exploded across Spain. Podemos is a direct answer to growing distaste with the austerity politics coming from Madrid. There are good reasons to have hope that they will succeed in next year's national elections, but there are reasons to be concerned.
First, the party has a highly ambigous position on the nationalism issue. The consensus decision making model they've inherited from the indignados empowers extremists, and could pose a serious problem for the party as it runs in Catalan regional elections. That said, it will probably return 10-15 seats in the Catalan regional assembly.
Polarized Pluralism
The great danger facing Catalonia in the coming elections is the specter of polarized pluralism. Largely absent from modern politics in developed countries, the idea has its roots in the proliferation of small extremist parties in 1930s Europe that emptied out the political center. As support for the center disappears, parties have to move to the fringes in order to compete. Arguably, this process has been underway in Catalonia, lending credence to the whole hypothesis of viewing the present through the prism of a postmodern 1930s. Let me explain.
Below I've tried to arrange the parties represented in the Catalan parliament from left to right. I am only interested in the nationalism issue, so you get oddities like placing CiU to the left of PSC. The following is meant more as an analytical model than a holistic depiction of reality.
Let's start back in 1992. This was the last year in which CiU was able to form a government with the support of a coalition partner. As such it represents the apogee of the two party plus system which existed in the region. For consistency, I am using present party names.

In 1992, CiU eked out a narrow absolute majority. More importantly note that over 80% of the seats are held by one of the two major parties.

Fast forward to the 2012 elections. Note that only 52% of seats are held by one of the two, traditional, major parties. CiU is pulled to the left, in this case that being towards greater support for nationalism by the need for ERC support to form a government. The center is flattening out, while the fringes are rising.

Fast forward to the present. With less than half its mandated term finished, snap elections appear to be on the horizon. The trend only progresses further. I've distributed the seat return away from the center towards the fringes in order to demonstrate the greatest potential for polarized pluralism. Seat returns are based on the latest poll.
I haven't included Podemos here, because I honestly haven't a clue how they will fall on the nationalism issue. My gut tells me that they end up in the same space as ICV, if not in an electoral coalition with them. This is but one of several potential hiccups which exist. Looking forward to the coming national elections in Spain, my feeling is that C's is going to run together with UPyD, a similar party from the Basque region. If so, that probably drains support away from PPC in these elections, as I expect the news of a formal relationship to break before any snap election. As I mentioned at the beginning of this article, the coalition between Convergence and Union, which forms the CiU, is beginning to crack. This is the center of Catalan politics. In the best case scenario, the CiU/PSC share of seats is likely to fall to less than a third. The center has fallen.
Now let's talk about the dirty business of forming a government. The magic number is 68.
2014 Seats
CUP 5
ERC 34
ICV 8
CiU 26
PSC 15
PPC 17
C's 18
Podemos 12
A grand coalition of the center (CiU, PSC, PPC) only gets us to 58. Really a non-starter. I can't see Podemos participating in a coalition with any of these parties, and even if they abstain, that's still 60 against to 58 for.
Assuming that CiU can enter another nationalist coalition without fracturing, there is a path via CiU-ERC-ICV-CUP to 73 seats. Yet, this is unlikely, as it would almost certainly fracture CiU. Moreover, at this point ERC and CUP are pretty much radioactive. With the exception of ICV and maybe Podemos, they are going to be on the outside.
So let's kick CiU out, and bring Podemos in. An ERC-ICV-CUP-Podemos coalition only gets us to 59 seats. Even if PSC abstains, that still leads to a 59 for, 61 against failure.
Please play with the numbers. I just don't see a viable coalition emerging, which means new elections after this coming set of snap elections. That augurs further drift to the fringes, further polarized pluralism.
Conclusion
What to take away from this?
There's a fleeting possibility that the CiU attempts to replace the support from ERC, with that of PSC. That gets you to a coalition of 70, and the unending enmity of the fringes. It only postpones the problem, and probably not even until 2015, as there will be national elections in Spain at some point in 2015. The same polarized pluralism which is manifesting now in Catalonia is developing at a slower rate in the rest of Spain, where the two-party share of seats is set to fall to just over 60%. An electoral union between UPyD and C's presents a right counterpart to Podemos on the left. Using Podemos as a template that would drop the two party share of votes, and seats, to well under half. Competing for support from parties of the fringes forces the parties of the center to the sides.
Wash and repeat for a postmodern 1930s.