One of the recent interviews had one of the devs saying Republics are out of the game because "it's an entirely separate layer of gameplay. It doesn't really interact all that much with the feudal heart of the game."
That is a worrisome thing for fans who enjoyed the non-feudalistic part of the world, and those of us who desired a game that can better simulate the fun of being an administrator in an empire or republic. All the reveals so far have been about "deeping depth" and trying to create a better feudal gameplay.
However, that might make it even harder for them to simulate the non-feudal part of the world. The Byzantine Empire will once again become a feudal empire if the game mechanics are not properly designed.
I think they're leaving republics and certain forms of governing to expansions, which i don't really have a problem with, also they probably have alot to think about when it comes to republics, like how to handle titles within a kingdom-title republic, should citys and castles go to the current leader of the republic, or should they go to the leader of the house that conquered/created them, should patricians have a smaller domain modifier than feudal lords, should there be different republic goverments, and how should the elections be, should it be based on popularity + other factors, should they simulate a senate/magistrate, as many republics often had.
The republics can be absolutely fantastic in this game, but not if they're quickly created, i'm guessing one of the first DLCs will be republics.