Switching to real time requires overhaul on encounter basis. Realtime gameplay tends to have more encounters. It would require huge amount of work for modding team.
But why conflate two separate things? Balancing encounters is completely separate from creating a RTwP mod. I would be fine with a mod that just only enables RTwP combat and nothing else. All the talk of how encounters in TB games are "hand crafted" and "unique" and so on are complete nonsense to me. I have yet to see a single combat encounter in a TB game that was in way better designed than such encounters in any RTwP game.