In some of my ideas screwing around with fexp/fan games I was thinking about making people that turned into baels (those giant spiders in fe8). And was planning on letting the player get one at some point on the team, they would be similar to the sub-humans from fe9-10, or wolfskins, kitsune, etc.
I also thought it would be cool to have a best rider unit besides the horses the goes on the ground like a boar or something. Not sure if that's helpful or not, but I think it would be awesome to have some classes like that in Fe Esq game.