MK9 makes the most sense by far.
MK8 was a visual showcase for both the Wii U and Switch, so it’s the perfect chance to really show off the new hardware. The demand should be huge too after such a long gap, which is exactly what you want for a new system: an exclusive game with huge demand. It’s a no brainer to me.

I have also been hoping we might get a full remake of OoT as a launch title, since it’s going to be a very long time before we can expect a brand new mainline game after TotK.

Zelda: Tears of the Kingdom (depending on when it launches)
Something original
Super Mario Galaxy 3 or Odyssey 2
Super Mario Kart 9
SPIDERS!!!
Maybe a Fit game
Maybe an alternate racer: Excite something
Probably a casual game of some sort like Animal Crossing, Brain Age, or something along the lines of the 3DS Streetpass games.

Outside of the obvious ones (Zelda, Mario, an original game, and Kart), I don’t really have any interesting. Usually if Zelda comes out early, Mario is the following holiday season… vice versa.

Switch sucessor to call Nintendo Module.
This time selling other optional controller to attach instead of only joycon.
the controllers would offer a unique gimmicky experience. And would be a new game for each of them. Some at launch.
I think is the way to Nintendo always trying to being New experiences(as they alway say they have to do), but without build the entire console around it, and do not lose the sucessful form factor of switch.
Some games would support Some of these controllers.
MK9 with many of them.

Also, VR would also be an optional Module. And metroid prime 4 would support it.
But probably not on launch.

Diddy Kong racing + New Mario 2D game or keep it and cancel your next console

Love the alternative console answers! Much better and in line with Nintendo's spirit than simply "build similar, but better and stronger console" crowd we've got so far 

What I think it's launch games will be?

-Mario Kart 9

-Metroid Prime 4

-New 3D Mario

What I hope it's launch games will be?

-New Donkey Kong

-New Star Fox that doesn't suck

-New F-Zero

I think a 3D or 2D Mario will come out this fall so I'm not really sure if that will be an available option for them due to turn around.

Mario Kart I can definitely see, the main MK team has been free for a while, the DLC tracks I believe are being handled by a younger subset of the main team and the senior team members are just overseeing their work.

I'd expect more 3rd party support earlier in the product cycle too since the Switch concept has proven to be successful.

There's probably a shit ton of PS4/XB1 era content that a lot of devs would want to bring over and also titles like Street Fighter VI that would make sense (3DS launched with SSFIV).

Final Fantasy VII Remake, Elden Ring, Red Dead Redemption 2, Resident Evil 4 Remake, Street Fighter VI, Call of Duty latest game, Madden NFL I could see being on the next Switch as IP that aren't on the current Switch, several of them maybe even very early on.

Mario Kart 8 Ultra

Yeah true it would be great if some big AAA PS4/XB1 games were ported to Switch 2 for launch day. For example Street Fighter and Elden Ring, along with 3D Mario on launch day, and then MK9 and RE4 Remake a month later would be a pretty epic launch.