The religious difference between the Dutch of Netherlands on one side and the Flaemish or french-speaking of the south was a key factor in the separatism that would give birth to Belgium.
The religious differences between the Netherlands and Belgium generrally are greatly exaggerated. 1/3 of the Netherlands was also catholic and not just the south. There were many catholics in provinces like Holland, Gelderland and Overijssel. The linguistic differences were exaggerated too. The Dutch upperclass (and the royal court) spoke as much French as the Flemish upperclass (and the Walloon upper class). I believe that even the cultural differences weren't as big (the cultural difference between someone from Gent and someone from Rotterdam are not bigger than the cultural differences between someone from Rotterdam and Friesland; the people in Friesland even speak a different language). The various differences between Belgium and the Netherlands were exagerated to create more of a national identity after independence, which makes sense: why become a different country if you are not that different.
That said, the Belgians did have many legitimate grievances and it was completely understandable they revolted against the Dutch king. I just believe that with a more competent Dutch ruler (and crown prince) the whole revolt could be avoided and Belgium could have remained part of the Netherlands (and I realise that the Belgian poster will disagree with me).
But does that mean Belgium is an anomaly, an artificial country that never should have existed and would never exist unless by force from outside nations? Of course not. Having a national culture that completely differs from neighbouring countries is not a condition to become an independent country (although people here often think it is, just look at how often Belgium is split between the Netherlands and France); that would mean that countries like Luxemburg, Slovakia and even Canada don't have the right to exist. They do! The thing is, you don't need a lot to have your own different country. The only thing you need is to want to live in an independent country. The Belgians had that and managed to convince the Dutch that they had that and now they live in a different country than the Netherlands.
This could easily happen before it united with the Netherlands. It wasn't as if the Netherlands was so different from the rest of the Holy Roman Empire when they became independent. They decided they didn't want to be part of it and after the treaty of Westphalia they weren't anymore. The exact same thing can happen with Belgium. If the United States of Belgium succeeds somehow, the Belgians have their own country and will probably keep it (unless some other country, like France, succeeds in absorbing it agaist their wishes). The Wittelsbach idea has the problem of remaining part of the HRE, but I believe that the Belgian culture differs enough from German (because of the French and Dutch influences) that it is possible it won't get involved in a possible German unification.
So could we see an independent belgium before the French revolutionairy wars? Yes most certainly we can. The biggest problems are: how do we convince either the Spanish or the Austrians to renounce it? and how do we avoid it being gobbled up by neighbouring countries (and mainly France)?