I can see Metroid Prime 4 being a port or cross-platform game with bumped up performance/graphics in the same vein as Twilight Princess and Breath of the Wild. F-Zero I think we're WAY due for at this point. Especially since it would mesh well with a robust online mode and DLC/online service that suits the modern era of gaming and that I think Nintendo will focus on. We're also due for a brand new Smash Bros and Mario Kart.
These are largely pure speculation/hopium on my part but I think at least some have a decent chance of happening, the ones towards the top of the list moreso:
1. Star Fox
2. Splatoon (maybe reworked as more of a hero shooter a la Overwatch or Marvel Rivals?)
3. Mario Maker (with battles, competitions, more fleshed out online multiplayer)
4. A truly seamless, open-world 3D Mario (maybe with a branching world map with many pathways a la Mario World)
5. Gameboy Mario title Remakes
6. "Switch Play" (Wii Play on roids basically - with a variety of new and revamped mini-games, robust online content, timed events, DLC and such)
7. Mario Sunshine (remade to be a lot flashier, more open world, and easier)
8. Animal Crossing MMO
9. Star Tropics
10. Mario RPG 2 (a true Mario RPG SEQUEL collab by Square and Nintendo, not Paper Mario, Mario and Luigi, another revamp, etc)
11. Eternal Darkness (co-op and online gameplay, more open-world)
12. Earthbound
Beyond the Mario Kart, Metroid Prime, F-zero entries I mentioned though, I don't quite know what to expect, but definitely excited and curious to find out. Feature-wise, I can see Switch 2 incorporating more and more advanced AR features - think Pokemon Go on steroids. We'll also get more diverse and dynamic controller options, maybe even some customizable. A much more dynamic online system (finally) but still with safeguards to protect children. I think there will be a lot more of the limited-time "event" freemium and paid content, think Mario Bros 35. I think Nintendo and its 2nd (and possibly some 3rd party exclusives) will be delving more into BR, open-world, and roguelike stuff to tap into current popular genres and popular indie stuff. I don't see Switch 2 being a massive revolution in gaming, more of an evolutionary step. I think Nintendo is going to rely more on online game services/DLC/features and just a flood of 1st, 2nd, 3rd party and indie games to keep the money rolling in and to remain strong in the industry.
Hopefully we'll know a lot more by summer of '25, with a release of Switch 2 of spring '26 (though I can even see them waiting as long as spring '27 and even predicted as much years ago in another topic I'll never be able to dig up :P). I think Nintendo is still holding off b/c the Switch is still selling fairly solid and the shaky economy.

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