So everyone's already been over how the screen could either be from Smash Run or the Reset Bomb Forest. Personally...I'm kind of hoping it's the former.
From what we've seen of the Reset Bomb Forest, both sections are mid-size, meaning there'd be a lot less room to maneuver around the Orne than there was to avoid the Ultimate Chimera in New Pork City. Something like that could kill the stage's tournament viability (I know it doesn't have to be, but the more stages we can use competitively the better, right?). Smash Run has a gigantic area to run around, and dying would (as far as we can tell) only make you drop some of your powerups and have to rush back to them from wherever you respawn before an opponent can steal them.