So far, Titi and Softcoder have had the final say o what goes into the mod downloads. I don't know all of these factions, but if someone will prepare variants of them which are properly packaged techtrees and meet the formal criteria (or they already do) then they sure should be added. Note that some of these are already available on the mod menu (Prax, Japanese, Imperial).
The same goes for techtrees which combine two or more compatibly-licensed factions, where balancing changed have been applied (to make them compatible) and tested (for more than 5 minutes).