I'd like a 2-d boss option for bosses outside of the main 2-d Mario games. Like Dementio from Super Paper Mario, or Rawk Hawk from TTYD.

A world map to put your levels on, that would be amazing. Funny thing is they basically have the basics for this to port over in Super Mario Run.

There were a lot of great levels that made use of the limitations and quirks of the de-spawn system (to use more than the normal allowed maximum of certain items per level) so I guess it could never be 'fixed' for the first game, it would break levels. There were some nice mind benders because of that, especially after you became conditioned to certain things normally not being possible, or actively having to 'break' a rule to finish a puzzle.

And indeed what cycycychris said, more vertical freedom!

I hope the online is more fleshed out when it comes to browsing for levels and viewing detailed information about the levels. I liked the idea of showing the player who beat each level the fastest, and seeing where the deaths occurred. Putting together an entire 32-level game within SMM2 would be freaking sweet, and I'm really hoping they include this feature if not any others. I played through people's levels in a certain order in the original SMM to emulate the feeling of playing a full game, but it's not the same when lives don't carry over, and if you get stuck you can just skip the level entirely.

Otherwise, I really liked SMW as a kid, so chargin' chucks felt absent.

Damn that would actually be such a good game mechanic! You could create a lot of fun switch puzzles out of that.

I'd like to see Cappy introduced. getting to play the game as any enemy would be really cool.

yeah, I guess it might be unnecessary to have it then, eh?

Vertical levels are all but confirmed by the GameXplain analysis. They reconstructed the vertical scrolling portion from the trailer, and showed that it could be done in Mario Maker 1, but only if scrolling began and ended exactly with the clip in the trailer and only by utilizing every tile of vertical space, so if the level in the trailer continued for even half a second more, that would require more vertical space. So almost certainly we're getting vertical levels or at the very least more vertical freedom.

With the new 3D World style it seems very possible. Would probably be the most interesting powerup they could add, in terms of creative potential.

Yeah but those were just costumes. An actual 2D Odyssey style sounds like quite a stretch, as cool as it would be, but if they did, Cappy would be way more interesting than the Mystery Mushroom.