Nintendo always looks at how players interact with their games. Usually every generation changes things up a bit to try to offer a new gaming experience to seduce players to try out the new thing. Let's see how interaction has evolved over the generations:

NES: D-pad, 2 buttons
SNES: D-pad, 6 buttons
N64: Analog stick, 4 player ports
GameCube: Second analog stick(C-stick), GBA Link
Wii: Pointer controls
Wii U: Wii U pad, Asymmetric play
Switch: Joycons (also linkable to Lite)

Gameboy: D-pad, 2 buttons (same for Color, so same gen for Nintendo)
GBA: D-pad, 4 buttons
DS: D-pad, Touch controls.
2/3DS: Circle pad.

Nintendo refers to the 'Switch2' as a new generation, therefore I expect them to have something new when it comes to interacting with their games. Now this does not mean I believe they are going to trow away the Switch Hybrid concept, but they are going to add something that the Switch cannot do or cannot do well.

So I have a theory.

Twice we have seen Nintendo introduce asymmetric play. With the GBA linkcable for the GameCube (e.g. Four Swords Adventures) and with the WII U pad (e.g. Nintendo Land). Both where commercially not successful. But I believe that does not mean Nintendo is not going to try again. I think Nintendo believes in the concept, just that the execution was wrong. So they are going to give it another try.

I believe the Switch2 will enable asymmetric play using other screens that you already have. Like other Switches (including Switch1 that is widespread now), but also other mobile devices like tablets and phones. You could say Everybody's 1-2 Switch was kind of a try out for that.

You can also use these other devices as a second screen. So e.g. imagine using a gen1 Switch lite as a controller, having the Switch2 docked to the TV. Launch games to utilize these features could be Nintendo land2. Ports/Remakes of games like Four Swords Adventures, Zombie Wii U and all kind of new party games could be made.

Additionally a simple $99 controller with a small screen could be bought separately, for people that don't want to give their tablets/phones to their kids or have no other switch devices around. This controller could even be a pack-in for Nintendo Land2.

What do you think? Or what other 'Gimmick' might the Switch2 have, or perhaps none at all?

An optional dock pro that substantially increases processing.

I hope it doesn't have another gimmick. Just improvements to the original Switch would be good enough for me.

I'd see some form of AI for the next Nintendo system, because it's the current big thing. Maybe they include a mic again in the controller and an AI helps you or makes you able to play the game with your words somehow.

A dual screen feature could also be possible. They actually included it in the Switch OS 10.0, but never used it (except for testing maybe).

A gimmick generally refers to the name and character of a rapper or wrestler. But I think you're talking about interface features.

I think it'll be the same as the Switch, mainly. Joy Cons - which are really an advancement of the Wii Remotes with interface options closer to the older consoles. I do think that they could add some additional interface features related to health products - we were hearing a lot about their QOL platform. In fact, it's a little curious that they didn't do that with the Switch, especially given that Nintendo saw a massive influx of people looking for interactive fitness products, and it ended up being a very underserved market this generation despite having a large audience that's willing to spend a lot of money on, and Nintendo is losing to companies like Apple and Peloton growing their respective interactive fitness platforms from a few hundred million in 2017, to billions of dollars today. Big missed opportunity for Nintendo in my opinion - especially considering Ring Fit and Switch Sports alone now exceed 27.5 million sales.

I always wondered why we did not see Ring Fit Adventure DLC of some kind. It would have made perfect sense. Either paid and/or included in NSO.

Perhaps the return of the vitality sensor?

Voice control of some kind would be cool and a great accessibility feature.

I did not know the Switch OS 10.0 supported dual screen. Interesting, perhaps laying some groundwork for things to come for the successor.

That would be cool, but I'm not sure that's where Nintendo's head is at the moment. But who knows?!

I think that would be good enough for most people. But I think Nintendo will not be able to contain themselves and feel they need to have a headline grabber of some kind.

I'd like to see them expand the VR aspect from Labo VR, it felt like Nintendo genuinely had a ton of ideas in that game that it was almost overflowing with content.

Which it won't match a really good VR headset, if Switch 2 has a 1080p screen it should be able to do something a fair bit better than the Switch 1 did with Labo VR. Should be enough to have optional VR play modes for Mario Kart, Metroid Prime 4, etc. etc.