User blog comment:David eric/3 characters slots and 3 stages slots! (3DS Version datamined)/@comment-25096445-20151003140822

Characters: Probably K. Rool, Isaac, and one more newcomer. I doubt Sakurai will add another veteran, plus, the Fighter Ballot was for newcomers.

Stages: Maybe a Golden Sun stage is coming, kind of like how Ryu came with Suzaku Castle.