Even though we didn't get it in the Direct.
Between both games getting packaged together on Switch 1 + the 2nd movie being given the Galaxy subtitle, I think it's a very strong possibility that the next 3D game will be Galaxy 3.

Isn’t happening.

Yeah i was hoping it to be called Super Mario Universe as the name.

Given how random it seems for them to make the next movie around Galaxy, I do kinda think it indicates the next mainline Mario is indeed a Galaxy successor. I don’t think it will be called SMG3 though or be that straightforward of a sequel. More of a successor the way that Odyssey is to 64. 

I think it will be doing a whole lot of new stuff but be set in the Galaxy world and be a similar style of Mario game with the gravity mechanics and all that. But maybe with a much larger scope than the two Galaxy games. I agree with the Super Mario Universe title as a name that would make perfect sense for it. 

The Wii did not have a second control stick for Camera control.

So Nintendo had to come up with an idea for a 3D platformer where the player did not need to move the Camera themselves and the Auto-Camera would suffice most of the time.

The Galaxy idea was a brilliant solution.

Eventhough now having a second control stick, there is still a case to be made for a game not needing it, because an auto-/fixed camera can be more entry level friendly.

I could see a new game using concepts and idea's from the Galaxy series, but not necessarily be a Galaxy game.

The Wii-Remote had a d-pad which was used for camera controls. Not just in Galaxy, but also in a bunch of other games like Monster Hunter Tri, for example.

The d-pad isn't different to what the C-buttons were on the Nintendo 64 controller. There's no such thing as a solution Nintendo had to come up with due to a controller. They wanted to make a 3D platformer revolving around spheres and that's what they did with Galaxy.

That's why I said "Most of the time". It wasn't a natural way of playing the game like e.g. in Odyssey. The natural way of play was to use the controller of the Nunchuck to move around and have the pointer to well 'point, click and waggle'. It's true that it worked like the C-buttons on the N64, but those camera controls aren't exactly great with a more modern game. Nintendo understood that and made the Galaxy games in a way that the player did not need to rely on them.

Just the same way SKyward Sword world was build with forward movement in mind for the same reason and therefore the 'overworld' seemed like linear levels compared to Twilight Princess. Only exception were sky and water levels, where the movement was so slow to have the auto-cam catch up. You could obviously center the camera with ZL, but Nintendo designed the 'levels' so to not have the player do that all the time (like Ocarina)

Galaxy was the first Mario game I ever beat. Sunshine I never finished. Mario 64 felt archaic to even play after playing Sunshine, though I did beat SM64 DS.

I never really thought of Galaxy as difficult *shrugs*

I'd bet against it, but wouldn't be totally shocked if it happened.

As somebody who has 100% completed every mainline Mario games more than three times, there is no longer such thing as a difficult Mario game for me lol. I remember really struggling with Mario World on my first playthrough, and SM64 definitely had me yelling (b/c Mario moves too much when turning while stopped), but other than that Mario has never been too much of a challenge for me.