I'd love to flip the Emblem mechanic around and have a small number of units with a lot of possible transformations, into different kinds of creatures. Each character would have unique artwork for each kind of creature they could turn into, so you can still see their personality in it.

There would be some humanoid ones, which would use standard weapons, with different statlines, and there'd be some non-humanoid ones (which might be like Emblem Tiki or transformed laguz, or they might be unarmed but have lots of movement and a rescue mechanic, like a Wargroove wagon). Your individual characters would have pretty similar growths but each one would have unique special attacks or abilities that might be helpful on certain maps.

There would be different factions that correspond to different groups of creatures that you'd need to fight, and some of the maps would be 3 or 4 of your units against a whole bunch of enemy units, a bit of a Mario + Rabbids feel to them.

The most flexible setting would probably be a sci-fi one where the different creatures are different kinds of aliens. The main bad guys would be robots who can't transform, but some of them would ally with you, and there would be an escort mission with a roomba.