[mkjonesuk]

There are now cart dumpers that can copy and store multiple Switch games on an SD card. If the same form factor is used its likely these will still work for original Switch games.

[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.