I would love a fantasy or medieval/historical 4x RTS hybrid like Sins of a Solar Empire.
In fact I was hoping that Ironclad's Sins of a Dark Age would be that, but they went the MOBA route.
Basically, something like SOSE but instead of planets, and asteroids etc we'd have Towns, Cities and Fortresses/Castles.
Neutral capturable areas like mines, farming land, river ferries etc.
Obviously the map would be a little more open since phase lanes would not be a thing and choke points would be from natural elements like mountains and rivers.
I'd want soldiers to be in units, like in BFME or something, doesn't need to be 100's like total war. then instead of Cap ships you have Heroes or Generals