[jerf]

I would be unsurprised if the cartridge has the same form factor but has internal differences for Switch2-only games. If they want to try to lock Switch2 cartridges down more, there's plenty of ways to do that while maintaining a similar enough form factor for Switch1 compatibility.

[mmaniac]

NDS and 3DS cartridges had a similar form factor but operated by a completely different protocol. I expect Switch 2 to do something like that, given that piracy-enabling cartridge emulators for the Switch 1 currently exist.

[mattl]

I suspect the cartridge will be similar but have a notch on it that prevents it being inserted into a Switch console.

This is how Game Boy Color, DSi and 3DS systems handled being able to accept games from older models worked.