Good roster! I'd buy it just for Lightning, tbh.

I think Pyra would be better suited to a 'main' Smash rather than a girls-only spinoff, so that she could have Rex and work as a Blade-Driver pair. In her place, I'd have Elma. Not only would Elma make more sense as a solo fighter, I think she also has more potential for an interesting moveset due to using both dual swords and dual guns. Also it would generate more interest in Xenoblade Chronicles X and help Monolith convince Nintendo to let them do a Switch port and I need that in my life oh god please.

I'd rather have Blaze over Amy, but that's more personal preference than legit reasoning; I know Amy's much more well-known.

The Boss would be great, but unfortunately, I doubt she'd get in due to Konami. I have no idea who could take her slot, though. It's selfish reasoning again, but maybe Sarah Bryant from Virtua Fighter, to try and get SEGA to finally revive that series? However, there would then be three SEGA guests, so that would be too unbalanced.