Now that's a topic I'm more familiar with. I don't see Belgium falling apart anytime soon, for reasons I'll explain later, but I think it'll happen eventually. I speak with Flemmings regularly and this is a subject that comes up sooner or later. It's interesting to see that in the last few decades Flemish separatist sentiments have spread considerably through the political spectrum. Until the 1990s separatism was pretty much confined to very right-wing circles. As Flemish nationalism was strongly associated with Nazi collaboration during WWII, any party or ideology that kept their distance from the Nazis wouldn't touch separatism with a 10' pole. Vlaams Blok, itself quite right-wing, managed to change that. The moves toward stronger federalism that've been running through Belgian politics since the 1970s are a reflection of that.
The reasons the strings aren't cut yet are, as I see it, the following:
Wallonia needs Flanders in Belgium for financial reasons. Mining and manufacture, once the engines of Belgian economy, were mostly located in Wallonia, but have largely collapsed since the 1970s. Today Flanders is the rich part. Consequently, the Walloon part of the electorate will resist separation to the end.
Flemish separatism is still much a right-wing thing. Socialists and, to a lesser extent, liberals aren't very keen on the thing.
Even if splitting Belgium in two could be negotiated, there's the problem that both sides want Brussels. No political settlement is possible in which either Wallonia or Flanders get Brussels.
What's the perspective for the resulting parts after a split? Separate states? An independent Flanders I can just imagine, but nothing like it for Wallonia or Brussels. I ignore the German speaking minority in this discussion. I don't think Wallonia is keen on joining France and integration of Flanders in the Netherlands is something neither the Flemish nor the Dutch fancy much. The Flemish haven't forgotten 1830 and will not become subjects of an Orange.
That said: Belgium doesn't work very well and the Belgians know that. The fact that it took a year and a half to form a new federal govenment after the 2010 general elections is revealing evidence for that. I think it's inevitable that somewhere in the next twenty years the knot will be cut, possibly along the lines of: Wallonia in some way connecting to France, Flanders as an independent state and Brussels as a European Capital Territory.
I can be wrong.
regards,
Hein