I think one thing that would be great from GranBlue Fantasy is the music. I also would love to see spirits of Ladiva, Lowain, Katarina, etc. I have friends who are super into GranBlue and tell me the lore is amazing. The music, of course, is Nobuo Uematsu, and that is a winner.
Moveset-wise I do like how they work in the fighting game...I'd love to see people be even more creative in adapting a mobile game moveset to Smash though.
(I think I'm doing this right)
Ichiban x5 (or 10? I'm not sure how many I get - maximum though, I wanna talk about Ichiban some day dammit!)