Oh, yeah, I tried to do a google search of civ fanatics for flavor units before posting about it, but this is something that interests me greatly. I've been kinda working on this on the side, having done half of Japan... albiet with PTW units (so the bix for the PTW version would have to come with a batch file or whatnot that could copy the files over... the way I did it turned out to be accidental, but it turned out really well: Medieval Inf, Samurai and Cavalry replaced by Taira, Minamoto and Nakamaro Samurai).
I have a great way to coordinate the actual workings of the project; Dom, if you'd like to collaborate on this, PM me. I think this would be a great project for nearly everyone to give input to; I happen to know a fair amount about the history of Japan and the Iroquois, but know hardly anything about ancient Celtic and Germanic history (my ancestors aren't too happy about that, I imagine
). So, by getting input from everyone, we can have experts on Rome, the Zulus, Greece, Persia, etc. help out.
Another interesting thing to consider when doing flavor units: giving modern units to ancient civs, and vice-versa. It's all well and good to give the Iroquois a NATO MBT, but it'd be really neat to design one of their own.