With how often they've mentioned wanting to "get it right" I would suspect a Byzantine Empire DLC would be one of the first they decide to do. Nomads, Republics, etc were taken out because not a lot of people play them (according to the devs) so I don't think putting them back will take priority over something they know people want (and thus will pay for) like an expansion fleshing out the Byz. But how long it takes to get made will most definitely depend on how the release is received. Personally, I hope it's good and everyone loves it, because I'd like to get the planned DLCs, whatever they are, out when they were planned and not delayed while they completely remake the entire game *coughImperatorcough*