Rosalina is a lock I think if the game DOES get new content that includes new characters, along with Wario. Both of them have natural abilities that lend themselves perfectly to SMR's one-hand, touch anywhere gameplay, and they would add a new twist to how you play the game. The question is whether or not the game gets updates.
Rosalina can retain her Spin Attack from 3D World. To adapt it to the no buttons gameplay though, they could make it that it only works in mid-air, and only works once per jump, and it refreshes when she lands on ground, on a wall, or when she bounces off an enemy. It still retains it's double jump effect though as well as it's hitbox, making her the perfect character for enemy combos. If they don't already have it in game inherently, they could make Rosalina get a special score bonus when she chains enemy KOs together.
Wario could get the Shoulder Bash. When he uses it, he gains extra horizontal speed and barrels through enemies/blocks in his path, but he loses all upward momentum as soon as he uses it. They could also make it so that he gets extra coins from defeating multiple enemies in a row, as a parallel to Rosalina.