MK8, and maybe a drastically revamped, properly advertised NSMB game that clearly wouldn't able be to be done on the 3DS/Wii.
I'm banking on the 3DS commanding SSB4 sales. The larger part of it's install base isn't gonna lose sleep over not being able to use a GC controller.
Bet with Einsam_Delphin: http://gamrconnect.vgchartz.com/thread.php?id=172355&page=11