Just my oppinion, but lets not include a bunch of fluff. I'd much rather have unique CIVS, maybe a change in the UN. So long as we have unique cultures lets not get anal. It's all about emphasis. The goal should be to remove the concept of race altogether, and emphasise the differences between various societies as a whole. So I'm playing mali and I conquer Rome are all my roman workers now black? Nope they are roman, and both roman and mali workers are HUMAN. Members of my society.
Do we REALLY want to go in this direction? Emphasising trivia? So your black for example (the racialist stereotype) are you Othello's sophisticated and exotic foreigner, or a subhuman civil war slave? It means nothing.
Best to leave it out, concentrate on what is important. Sure add in a segregation civic, like the caste system civic, add in a genocide civic, add in whatever you want with some gameplay meaning, but just different colored units? Are you going to give me green units so I can build a little green men civ? lol
Add that in last if you have to, along with the different city styles so I can build step pyrimids or eastern podogas again like in civ II.