I think building an RPG would be perfectly feasibly, simply because it means just removing half the game (city-building). You can play an RPG currently by just not building any cities.
It'd be pretty bad though, since you can't do much with tactical combat (no terrain bonuses, no line of sight, no flanking or any such things). Interaction with other factions would also be restricted to current mechanics and quests. Alternatively doing a scenario (allows for slightly more scripted things to happen on the world map), which equals non-random maps.