I don't see why not.
We saw Giant Death Robots and XCOM Squads in Civ 5.
Well, perhaps in the future era that could be possible, but not in the scale its presented here; players first city could be a water city on BERT, its hard to imagine floating cities that can move realisticly presented on Ancient era civilization. So even if they were added they only come in so late that they cant be as integral part of the game as in BERT.