-Isabelle for a Villager echo. She's popular, seems likely.
-Mona as a Wario echo. Just because it would be hilarious on a variety of levels.
-Waluigi isn't a playable character because he's "too tall."
-Cat Suit Mario, Raccoon Mario, Metal Mario, Bee Suit Mario, Penguin Mario, Flying Squirrel Mario as Mario echoes. Because you can never have too much Mario.
-Dark Metal Pit as Dark Pit echo. Just to make sure no one forgets Kid Icarus Uprising was a thing.
-An elaborate trailer which sets it up to look like an Advance Wars character will finally be playable, but turns out to be introducing Linkle as playable instead. Trust me, this'll make sense in context when you see it.
-Handheld mode features an all-touch control scheme.
-There will be a stage where you can rub the faces of the Fire Emblem characters.
-A new mode called "Street Fighter" will change it to where moves are executed with large button combos rather than just one button and a direction.
-Ganondorf is now a Fox echo. Makes sense to me.
-New playable characters include Sandbag, Target, Fighting Polygon Team, Fighting Wire Frame, and Off-Screen Kid From the First Game.
This is what I've heard from leaks anyway. Seems plausible enough.