First off, if 3D Mario isn't a launch day game that is a huge blunder for Nintendo. Nintendo needs to always launch with either 3D Zelda or 3D Mario, if all they've got is MK9 at launch that is a fail. So I expect we'll be playing the next Mario game in like 3 months.

No interest in remakes, every Mario game is already on Switch other than the strange exclusion of Galaxy 2 from 3D All-Stars, I expect them to release Galaxy 2 at some point but other than that Nintendo just needs to focus on new Mario games.

I'd like to see one of two options for the launch day 3D Mario: either a full open world game made like Bowser's Fury, or a "Galactic Odyssey" game that combines Galaxy's play with Odyssey's play to finish off both those formulas. Galactic Odyssey would be a mix of series of little worldlets with larger worlds like maybe most levels have a main planetoid but also have a bunch of satellite worldlets, and of course include cappy gameplay.

Of course I wouldn't mind something completely different that didn't continue Bowser's World or Galaxy or Odyssey at all.

And with a launch day Mario game, I'd expect one more 3D Mario 4-5 years later, 3D World 2. 3D World was soooo good it really perfected the 2D Mario formula (tho obviously in 3D). It would be a huge shame not to get a sequel to it, and at that point it'll have been more than 15 years since the original so it'll be a good time for a sequel.