I wonder why Belgium gets screwed in virtually every alternate history scenario!? Honestly you guys are forgetting that Leopold I and Queen Victoria were actually relatives and were actually buddy-buddy with each other. Also Britain guaranteed Belgium's Independence and protected Belgium. Lets not forget that Belgium was the ideal solution brought forward in the Berlin Conference to maintain a status quo in the African continent
Ideal for everyone who wasn't, you know, Congolese.
Part of the reason Leopold II gets dumped on in Alternate History, is that, frankly, he deserves it. The OTL Congo Free State was such a dystopia that people want to make it better, and the most obvious way to do that is not to have that moral monster in charge.
As for more general cases of Belgium consistently getting the short end of the stick, I hadn't really noticed it, but I haven't really been keeping count. That said, Belgium usually only gets mentioned in the context of a United Kingdom of the Netherlands (which has the appeal of looking nicer on the map), World Wars I or II (and for whatever reason, timelines about either of those two tend to be about German victories), France going on a massive conquering spree, or King Leopold (as discussed).
It's hard to imagine a Belgium that becomes enormous, although if you have an idea, by all means feel free to contribute (the other problem being that people know their own country best, which is why there are a plethora of American or British history WIs, and fewer for other countries).