First I would like to start out by saying that CA has done a great job, in my opinion making the new faction rosters. The four newest factions feel fleshed out and well-rounded, plus they all have pretty good roster depth. That being said, there are two major things I would like to see touched upon if Rome II is going to continue getting content.
1. Please dear sweet Jesus fix the Balkans factions. Its laughable how badly these rosters are put together when compared to the newest DLC factions. I realize that this is likely not going to happen, but it would be extremely appreciated.
2. Some areas of the map still feel weirdly glued together to fit the province system. (Looking at you Numantia.) Not only do large portions of the map like Iberia feel relatively empty with giant one off regions like Numantia, other regions of the map have now been made weird by the addition of the newest DLC factions. North Africa, in particular the area that Massaesyli start in could use a few new towns. These regions are huge and almost entirely empty. There aren't even resources in most of them. On top of this, Nabatea's starting province now feels even weirder than it did with Jerusalem being the only city they don't start with. Move Jerusalem to its own province, and add a small town in the Sinai peninsula on the Red Sea coast.
I'm sure there are other regions that I haven't noticed yet, but these are the ones that really stuck out to me. I'm aware that this is all likely a pipe dream, but who knows, I never thought Rome II would get more content.