Regarding Disney bosses, having Julius, who is obscure as it is - and I had no idea he even existed until hearing he was a secret boss here - as a secret boss is very cool. So many Unknown's and what not, it just felt generic to see the Unknown in BBS, as a simple hooded figure with light sabers, or a palette swapped Vanitas. I'd love to see the other Titans from Hercules (Lava, Tornado, maaaaybe Cyclops), the Big Bad Wolf, the Headless Horseman, or even the Tyrannosaurus from Fantasia as secret bosses, since they likely will never appear.
Of course, the Unknown bosses (Xemnas, Terra, and the Unknown) have all turned out to be vital to the plotline, but maybe have a tournament Olympus style versus various bosses of Disney past, so the more important ones like Xemnas have the "Secret Boss" status? This could also be a chance to get the Frollo boss fight we were robbed of.
On the topic of Disney Vs Final Fantasy, I miss the Final Fantasy characters. While it was cool to see some variety this time around with TWEWY, how epic was it to fight alongside Squall, Cloud, etc in KH2? I don't think Disney has been shoved in our faces - obviously Disney has played an important role in the series (Mickey, Donald, Goofy, Pluto, Jiminy, Maleficent, Pete, the Princesses, etc), but in KH2 there was so much filler. Half of the worlds didn't do a damn thing to advance the plot besides more bonds of friendship for Sora. Kingdom Hearts 1 had a good balance of plot-advancing Disney worlds and Final Fantasy, and that's why the series became what it is today, because of its harmony in blending Disney and Final Fantasy. Two separate franchises became one in Kingdom Hearts - hopefully it happens again soon.