You can either predict what's the next new game announcement, or speculate all possiblities within the current console era.
So starting with sport/party spin-offs: the current game lineup on Nintendo Switch has covered most sport subjects from past consoles. The only big one remaining at this point is Baseball, which was released on Gamecube and Wii.
By record, it is possible for Nintendo to do multiple Party titles on the same console with different themes, but not sure if Nintendo change their mind.
And there is Olympics..... we don't know if Nintendo and SEGA are still able to work on this license in 2024 or they have lose interest in it, since we didn't get a winter title back in 2022.
But speaking of life circle of Nintendo Switch, I think there are still some potential to push new DLCs for the already released sport games. We didn't get too many DLCs on WiiU because its life wasn't long enough. I think Mario Kart 8 tried it, and other Mario games also have the potential to push it.
As for mainline: DKC obviously has the biggest demand for this console era, no contest.
Mario 2D seems very much enough with Wonder and other port expansions for now. As for 3D, I think there is a slightly bigger chance for 3D Land multiplayer series to get a new one, but not sure if it conflicts with the 3D World port. And not sure if Nintendo is still willing to do more single player games for either Mario or other main cast, or any possibility for new Captain Toad?
As for Mario RPGs: consider that AlphaDream is gone and no M&L sequels in forseeable future, we definitely need Nintendo to make more games beside Origami King within this console era.