It's time for speculation.
New Pokemon
>Deoxys
New fire emblem
>Lyn
Classic character come back
>Dig Dug
DLC's
>Alucard (from Castlevania)
>Mr. sandbag (from punch out)
>Shantae
>Helix (From ARMS)
>Rygar (from the NES Game)
New items
>The power glove: it summons a huge fist that causes 34.27% of damage but it only works 3 times
>Castlevania throwable Axe (an axe that works as a bommerang and does 12.03% each hit but it only works 6 times
>Nintendo Labo Robot: it would be one of those items that are build collecting 3 different things but this time those things are parts of the Nintendo Labo Robot, when you have them all, you transform into the giant robot for 8 seconds
>A rubber duck: when you throw it to someone it would be like a water attack from any character that uses water
Eg. Greninja and the percentage would be that attack damage.
New assistants
>Space Invaders: they will summon a game if space Invaders but all the shooting including the ship ones affect everyone except for the one who summon it
>Chibi Robo: it electrocutes the opponents from a 2m distance
>Mario Kart Boo: steals opponent items
>Hector (from fire emblem): attacks with his axe
>chorus Kids (from Rythm Heaven): they sing so hard it has the effect of breaking shield on all the oponents
Just a wishlist but hopefully atleast one thing of this is added.