Linguistic identity is too singular. Actually, if I'm not mistaken there used to be national parties before the 1970s, when federalisation set it. But right now there are two completely different communities on diverging economic paths and with completely separated media environments. There is a Dutch language article about this in the Dutch daily NRC. A translated quote:

There is no Belgian media. A political scientist from Antwerp - Dave Sinardet - has researched how much attention there is in the TV news for events across the language border: 3 percent. Even French-speaking ministers of the Belgian government get little time in the Flemish TV, and vice versa. "It is de facto more useful for a Flemish politican to visit the pub around the corner on a sunday afternoon than to go to the studios of RTBF", Sinardet writes in a recently published book (What Belgium stands for).