Okay, do I even need to point out why this is an absurd suggestion? Because it should be pretty obvious.
A character whose only role is in a video game?
I think Dixie would work best as a semi-clone. I'm not sure she can be an echo fighter with her hair mechanic. The basic idea for an echo fighter is they could pass for an alt costume but have become a full fledged fighter (this is what happened to Lucina and Dark Pit). I don't think you could do justice to her hair attacks without being at least an Isabelle-level clone.
I'd love a Kumatora echo fighter though. I'd actually play as her over Lucas.
I didn't think Kumatora would feel right as an Echo Fighter until I saw the mod, all I'd need is PK Ground and I'd be golden.