At the Movies!

[CLXcool]

Even though its called 'Princess Academy' some of the characters that are in the concept art are NOT princesses. Surprisingly enough Jessica Rabbit would've been one of the non princess characters to appear. Her silhouette is shown in this piece.

I kind of wonder if they were going to go either full CGI or full 2D or just go a route similar to Gumball and feature both styles, given that Pixar characters were going to be featured as well.

My guess is as good as yours. Chances are they would've gone for the Gumball route and work in both styles. According to the Disney wiki, this only got scrapped because Princess and the frog didn't meet Disney's expectations money wise.