As someone who lives in Flanders but works in Brussels I have a somewhat strange perspective of how the two sides (ie Flemish and Walloons survive). Both hate each others guts but both also admit after the usual 5 rounds of slagging each other off that neither can live without the other. The Flemish have more people and the commerce, the Walloons have more land and energy sources.
The problem is that since 1831 (the creation of Belgium), the Walloons have always been topdogs. onlyin the last 10 years or so have the Flemish reversed this status quo. It is only the monarchy - who are adored by both sides - that is really keeping the country together. In Belgium - and I have experienced this first hand - you can insult a Belgian's wife, sister, and region, but you do NOT insult the Royal family. A refreshing change.
Also, much was made in foreign (ie non-Belgian) press about the break up following the 180 odd days of no federal government. Everyone still paid their taxes, all the schools stayed open, the bins still got collected (weekly I might add) and no-one noticed any difference...life went on as usual. This may be because most power is devolved to the the Flemish and Wallonian governents which will explain why the roads are better in one aprt of the country than the other - funding is different. For example, one out of every 7 euros in Flanders goes into education. In Wallonia it is one in every ten - hence Flemish schools are, on the whole, better than Wallonian. It also explains why in Flanders they can speak Dutch, English German and French whilst in Wallonia, they speak French and a bit of Dutch. Different regions, different priorities. As per Scotland and England.
As for Flanders joining Holland and Wallonia joining France...they don't want to. France had aan unofficial vote as to whether they would take Wallonia into France..yes they said. Most Wallonians said no to joining France, the same for Flanders joining Holland. One of the reasons is religion (holland is protestant and Belgium is catholic), the other is, I think, pride. Belgium fought hard to become independant from Holland and has never wanted to be French.
Two seperate countries with an independant city state of Brussels? Never. Both sides want Brussels.
It don't think they will spilt for the pure and simple reason is that if it did it would open the flood gates for Scotland, Catalonia, Basque to split and will cause grief for the EU - they will have to make a decision.
The Belgians can be bloody minded but not THAT bloody minded!