Hum, there is one. At least in my file for the release version, there is nubian factions beginning in 2650BC. As for a special faction in Nubia, there is one for the 1600 and 1450BC start dates. The first one being the kingdom who allied itself with the Hyksôs, and the ine in 1450BC being a united Nubia against Imperial Egypt.
I will work more in Nubia for the part of the game after 2000BC, cause I have gathered a bit of sources that I have not yet implemented into the game.