After a first read, this looks like a wonderful game.
As a Pendragon freak, my first thought is to use this for a campaign in Sub-Roman Britain, mixing history with the Arthurian myth.
I'm not sure I get the point of the whole "our world, but not our history" approach. To me the appeal of the game is in the setting of the Fall of Rome, so I don't really see what is to be gained by making it more vague.