It wouldn't surprise me if the asymmetrical gameplay idea happens; the ability to interact with Switch in many ways would be great. I would prefer if the unit was just a solid body design this time though with nice sticks/buttons and better ergonomics, able to sync existing joycons to it for table-top play or whatever.

But as far as guessing new additions I'll go with clickable scroll wheels added to the controls.

Hard to compete with Apple given they have a device (iPhone) that people carry with them all the time and even Apple Watch is quite popular and common these days too ... the best fitness device is one you have with you all the time (to track steps walked, etc.). It would be a pain in the ass to carry a Switch around to track all that. 

Peloton is struggling massively right now, their stock went from like $159/share during the pandemic to now being only $4.35 (yikes!). Total pandemic boom product. 

Fitness is a lucrative market, but it's very much a boom/bust market too, even Nintendo found out the hard way that all those Wii fitness buffs did not come back for Wii Sports Club and Wii Fit U. 

As far as I know, Nintendo sold a few million LABO packs in total, so I could see them continuing this in some shape or form. Good idea!

Clickable scroll wheels I can see. What kind of game applications could you imagine? I'm thinking perhaps a rhythm game where you can use the scroll wheels to match the pitch.

They could do the exact same gimmick the Switch 1 has, just with better hardware to support more multiplat games, and they'd be golden.

Functional joycons.

But seriously, no gimmicks are necessary. Just a stronger switch is enough.

Nintendo reuses ideas like this all the time, they experimented with 3D before the 3DS and were trying a 3D screen on the GameCube too which never got released. 

So Labo VR morphing into something bigger later on would be very much in line with how they traditionally do work. 

Super FX chip on the SNES no doubt was a testing ground to ease Nintendo into 3D development for the N64 also. 

They filed a patent that would suggest the type of thing you are talking about could be possible with a future machine. I think that's something that may very well be a feature, but not like the main selling point. Sort of like Street Pass or HD Rumble or something.

I think the Switch 2 will have some kind of gimmick. My best guess is VR as a third/fourth mode of play. We saw with Labo that you can get functional VR with a few cents worth of cardboard. Packing in a cheap plastic headset would give you pretty functional VR, and you already have detachable motion capable controllers, so it kind of makes a lot of sense to me.

VR is too limited. Only a handful of games support it and the cost of entry isn't cheap. I get a nice gpu is expensive but it supports thousands of games. Only 2 to 4 VR games even peak my interest.

Inventory button, scroll to what you want and click to use / equip