Bring For Glory back but give it some basic customisation options. You can pick between 1v1 or 2v2, Battlefield or FD stages, and the amount of stocks and time per match. But items and normal stages are always off. It will never give you a match that isn't your preferred ruleset.
Move all GSP related affairs and Elite Smash over here, and tie nothing to Quickplay (aside from the Challenges that are already tied to it, they can't do anything about those and they can all be broken with hammers anyways). Quickplay stays as it is.
Literally the only reason I ever feel frustrated in Quickplay, aside from the odd laggy game (it hasn't been too bad for me in this regard) is because I kinda want to do Elite Smash at least once, but if it's not FFA games, it's what seems like a 1v1 FD stage (I prefer Battlefield but I'll take it) only for me to knock an opponent away and a Smash Ball suddenly spawns near them and now I have to turn my attention to the Smash Ball. Quickplay shouldn't have ANYTHING tied to it, no rankings or special Elite Smash club. It should just be for people who don't mind what kind of match they play. And when I played it like that at first, I was actually having a lot of fun just messing around with different characters.
So yeah just put a For Glory mode in that's just a more restrictive derivative of the current Quickplay and move GSP and Elite Smash over to that. Keep Quickplay as it is with the exception of removing the ranking stuff.