I only see mention made by Blue that hags (EDIT: and half-golems, missed that) would be a power issue, and that's fine. Additionally, EO is still here and working on stuff (he's responsible for the Avenue du Progrés and partly the Grand Opera National), and he more or less designed many of the MPCs templates that are present already.
Broken Ones would be another good potential MPC/AMPC template to implement, and would certainly give people who wanted to play an aberration of some kind something to work with. Ideas are numerous: poor sailor who washed ashore onto Markovia and got transformed, perhaps? Or perhaps one of Elketh's experiments, escaped?
Edit: Would any construct like flesh golem be possible? Really we could do with some sort of Created monsters, I think, being playable MPCs, even if half-golem is too complicated.