Triforce Heroes minus the required co-op, with leaderboards/time attack for every stage, lots more cosmetic customization, a hub town/lobby, and optional co-op challenges.
Hmmm...
I wonder if they could also do a one-room type deal, just really simple and "get out as fast as you can!"
Although there'd be less leaderboard fun there, I'd imagine, as there'd be less room in the shorter challenge to separate people and within which to improve.
Especially if it were just figuring out easily repeatable puzzle solutions. Combat, extra space, alternate routes, using gear to trivialize, sequence break, etc. all could add room for a leaderboard to exist.
Edit: my point is even if it is ultimately non-obvious as to how or beyond a player's skill to get the best times, you'd want there to be obvious ways to improve your time.