3D Mario team haven't had anything since Odysee. I'd say that and Retro's Prime 4 as launch games. MK8 to follow soon after and surely Animal Crossing will arrive earlier than New Horizons, with the team alsp being the Splatoon team I'm guessing we would get a "deluxe" version of 3 before the first holiday season too.
I think Nintendo have slowed down quite wonderfully at this point - you don't really notice it, which is a far cry from the Wii and Wii U.
The Wave Race Easter egg in Pikmin 4 hopefully an actual tease - WR64 really is one or the most joyous games I've ever played and Nintendo would surely have much to pour into a new one.
I think there are plenty of GameCube games they could port up with F-Zero being the most obvious to truly test the waters for an actual new one. Kirby Air Ride is another I think they should think about given how Forgotten Land has ended up invigorating the IP. I know the context of ports was very unique with the Wii U, but I can see discerning usage of them being done again (and they are par for the course across all platforms now anyway, but Nintendo do seem more careful and/or deliberate with them).
And just going off topic here, I really did want Rare Replay on Switch. Honestly, I can see myself getting an X just to play that and the Horizon games soon enough.