Considering recruitable generals, because that does seem pretty cool, but if possible restrict to capital.
More formations for more units
More mercenaries (can never have too much mercenary variety, realistically it's kinda strange that the variation is so low. I remembered once upon a time I'd made a mercenary hastati, and I wanna do that again.)
Faction start rebalancing (give the greek cities more greek colonies)

If possible, remove the culture issue from buildings and reduce the distance to capital penalty. Neither make much sense and have zero impact on the AI. Honestly the game would only benefit from them being removed but I understand they are there to slow players. However the base rates are so high that playing late game becomes a drag out.