What about making a module of Caverns Of Chaos, where the players get to play as monsters? It's Chaos after all, isn't it? Why would their forms be limited to change into dwarf, elf and human only? And at the nightmarish modules, instead of having a chance to play with legendary characters, you could get to play with big figure monsters. I bet that would be really fun and it would also help new players get familiar with different monster types and discover new card synergies and strategies. It wouldn't be that hard to code, would it?
I don't think that it would be hard for the developers to code since we do have MM and in MM you play as monsters.
Technically speaking, after round 1 you ARE playing as monsters, just ones that look like PCs. And I've been asking Flax and Jon to add the CoC decks to the scenario editor so we can use them in MM too.
It wouldn't be hard to code, but it would probably be nigh impossible to produce an interesting gameplay experience. Monster strength is soooo disparate.
If monkey warrior drew 2 cards, and had some more HP it could make an interesting player character. Stout Maple Tree might be an OK player character.