Sounds like a Smash Bros RPG, but more properly focusing on the worlds of the games, rather than the "world" that Smash Bros has conceived for itself (which was the main problem with Subspace Emissary).

so Brawl as an RPG?

I would love to play that.

And I would love it even more if it was scripted as Fire Emblem: Radiant Dawn...

With each chapter, you change the group you get to take control of, and also the world in which they are located. In the final chapter, they all get together and fight the final bosses.

First chapter, Mushroom Kingdom: your squad being Luigi, Peach and Yoshi.

Second chapter, Corneria, with Samus and other characters from Star Fox universe.

Third chapter, Hyrule, with Link, Ike and other characters

Forth chapter, Gallia with Soren, Zelda, Micaiah, etc.

Fith chapter, DKC world with Diddy Kong, Mario, Dixie, etc.

Sixth chapter, Kirby's world with Donkey or Fox, etc.

I would love to see a tactical rpg out of it, but I'd be ok with an action rpg too!

Lol, it would be kinda like Brawl but there would be less characters and much more focus on the worlds. Just putting Samus in front of Hyrule Castle and call it a day wouldn't be enough!