Hi friend!
I have same ideas but I not know if you can achieve them.

1) Think you can grant to select General's bodyguard according to the conquered regions?
Is historically approved that generals and even emperors were using a foreign bodyguard, and it would be very interesting if a choice of particular unit may grant benefits to the region of origin of the selected guard, perhaps of public policy.
I think the same thing could be implemented with regard to the auxiliary units, remember that the auxiliary perceived wages and at the end of the service obteined Roman citizenship. Became part of the unit not only enriched the individual soldier but because of, also pays its area of origin.
This situation makes it more important diversification of hosts to secure a possible increase of consent even in the regions where mantaining public order in more difficult.

2) Is there no way to implement the right of citizenship?
I think it can be very interesting to be able to allocate at a Population the right of citizenship to make it more fluid and varied behavior of the Senate, it would be nice if at same point on the game a General born in Gaul arises as a new influential Family in the Roman world.
Think you can replace "other houses" with specific new tribes that have gained citizenship?
It might, in your opinion, be granted under the cultural conversion or something else?

3) It is still impossible to attach a Client State in, which cultural conversion has exceeded a certain percentage?

4) I know that this is an utopia, but you believe it is impossible to expand the park buildings and make it more specific by canceling the regional breakdown an recreating individual cities like in Rome: Total War?