This is a newb talking so take it with a grain of salt but

1. From initial videos it looks like when you pull out then put the cart back in, it seems to swap between games. So guess is that for the switch it looks like a normal game, not an initial boot interface to swap between, but what boots depends on which one the cart is chosen in the loop.

2. You're right it would be their own type, and likely a converter between them assuming the team doesn't put some sort of proprietary stopper

3. Likely the switch itself won't know the difference, but Nintendo has dealt with this problem in the past with the 3ds. They add a unique code to every game, so when you pirate it and try to download and update Nintendo can see 1000s of downloads of the same game with unique key, then they can just ban the console. Same if you try to play online (then later patching happened where you can change the key yourself). Downloadable updates where available then afaik