I just thought of another potential balance problem. China and ChoKoNu.
Right now they are the only ranged unit that can attack twice per turn or move after attacking (I know Chariot and Camel Archers can't, I'm not sure about Keshiks).
They are a very powerful unit, but it's balanced out a bit by them being the end of the ranged upgrade path and Barrage, Precision, and their multiple attack promotion become obsolete when they become Riflemen, but now all these promotions will carry over to Gatttling and Machine Guns.
Unless they changed the UU attributes from promotions that carry over to unit abilities that get lost with upgrades, every post medieval war against China has the potential to become a one sided bloodbath. Even if you're playing against an AI that can't set up proper kill zones, a garrisoned ranged unit with two attacks will make every city assault a costly and bloody business.