Yeah, I felt the same way. Did not want to buy the whole game again just for that bonus content. It's frustrating that we couldn't just upgrade our WiiU digital titles on the Switch like we did with Wii's Virtual Console especially since those digital purchases are still linked to our accounts...

The Galaxy games are still my favorite Mario games of all time.
So yeah go that direction.

My preference in this order
1. Super Mario Odyssey 2: If Galaxy deserved a direct sequel (and of course it did), Odyssey does as well. Luigi can be playable, Yoshi can be integrated like Galaxy 2, there can be a different villain than Bowser, etc.
2. Non-direct sequel to Odyssey that is similar
3. Super Mario Sunshine 2: I love the island theming and FLUDD is really cool.
4. Galaxy 3
5. 3D World 2 or a game like 3D Land and 3D World.

As someone who acknowledges he is not the target market of these games - and therefore my opinion probably doesnt matter that much - They should be "Galaxy style", so to say. Galaxy are the best.

Left right, up down, back and forth. All 6 directions in 3d space.

I have no idea what they could do. They've pretty much done everything. At this point, it's either change Mario so much that it won't feel like Mario anymore, or not change it enough.

Galaxy 1 might be the most fun game I ever played. I don't like the Odyssey style. Walk to that castle in a straight line and pick up 4 moons/stars/sunshines on the way. Unfortunately the Galaxy games visually don't hold up after playing Oddyssey. I would be ok with a remake of these games as well. Next to another new 3d Mario game

Galaxy > Odyssey, so I definitely wouldn’t be opposed to going back in that direction. But make everything bigger and grander in scale, from the galaxy sizes to the amount. Call it Super Mario Universe.

Just please no open world Bowser’s Fury type of thing. Not everything should be open world. Mario will lose its magic if they try to do BOTW with it 

Hopefully like Odyssey which is my favorite 3D Mario

The big question is if they go for a fixed camera or user controlled camera.

Galaxy 1+2 had a fixed camera, because the Wii lacked a second control stick. For 3D land/world it was easier to implement 4 player and one could also argue a fixed camera is easier for young/new players to get into.

With DK Bananza already being a free camera sand box exploration game and apparently solo player, I think the new 3D Mario will go in a different direction.

I think it will offer 4 player again, but this time could be a mix between galaxy and 3D world