2D metroid = meh.
Traditional Paper Mario = WOW! (bout time, those silly sticker paper marios, or platforming ones = meh)
A insanely good paper mario game (something that nintendo hasnt done in forever), could actually be a system seller.
2D metroid wont do anything sales wise imo. Too many indie games, are already at 2D metroid level or better.
Thats just a fart in the wind. It ll mostly go unnoticed imo. They would need to do a proper 3D prime metroid to get traction.