Will any of the figures who came to power in Croatia during WWII become prominent ITTL? The kind of genocidal nastiness and religious fanaticism that existed in the Ustase IOTL would not be out of place in the context of this war.
By no means an expert on Croatian history, but I'll find a few people!
Actually, the Croats remain fairly loyal to Maximilian right now... they obviously have no love for the Hungarians and would much rather remain a kingdom within Danubia.
Hmm...I suspect the Serbs (and behind them, the Black Hand) and Montenegrins might take this opportunity to go for a revolt. This will draw Croatian troops south instead of north, but honestly, this is not going to end well for the Serbs and Montenegrins. Especially if they decide to strike at Bulgaria and Greece as well, out of the former holding onto Macedonia and the latter stabbing them in the back during the war.
A good assessment- yes, the Balkans are going to go a little crazy (although that won't be for another few updates)
Well, assuming the Croations and Bohemians stay with the Hapsburgs, they could still do well out of the postwar settlement
Certainly neither have any interest in secession... at the moment. The coming influx of German troops into the empire will only further their decision to remain loyal.