So now that we have a new version out, before adding anything new there should be a focus on balancing what's already there, lest things get too crazy. Probably what should be done first:
-work out any new bugs that have arisen from past versions (the 0 city bug, disappearing cores).
-Balance the game situations for some civs (Persia)
-Balance the tech speed for larger civilizations so that they don't become insanely advanced in a short period of time (this is mainly directed at England, but I've also seen Portgual and the Netherlands become very advanced if they get large enough).
-Possibly rework the industrial tech tree to have a better distribution of units, or a way to discourage the AI from beelining.
Currently what I see is the AI always beelines the Steel-Railroad-Assembly Line-Fascism route, so that we end up seeing Machine guns in the 1820s and Infantry in the 1830s, when they should be coming later.