Theres an old game that i wish R2 would have taken after. It's called imperial Glory, and it came out around the same time as the original Rome. now, IG didn't have the best battle system like Rome (soldiers would happily shoot each other to the last man, and melee would have made R2's blobs proud) but wat it did have was a nice, well thougfht out diplomacy system. you could loan units to allies, who would actually request them sometimes, enemies knew when you were too strong for them to face. But one of the features that R2 could really have used was the peaceful assimilation feature.

Basically, you could do various things to increase your influence over a minor state, and if you reached 100% and had an embassy built there, the whole nation would join you, give you control of thier armies, and all thier resources. what was nice was that you had a motive to do this, since all the other major powers would also be trying to gain influence at the same time. Rome II's culture meter would have been an excellent way to implement this, and you could have client states that would give the option to annex them into your empire once you had enough cultural influence over them.

Just putting that out there, its a nice idea but i doubt it will happen.