would be so much better than custom games since you could find them easily and more people would bother to play it then
after you go to the quickmatch menu you could have to options, queuing only normal, only smash, or both (heres how it could look)
(edit) when you click on smash or normal, it deselects/selects it, you would be able to queue both at the same time or just 1 of them.