>to be fair, they might get something out of the anti-circumvention clause of DMCA

Nintendo's entire case rests on DMCA 1201. It entirely circumvents (pun intended) the reverse-engineering case law[0] most emulation developers point to. In other words, they aren't saying "you can't write a Switch emulator", they're saying "you can't tell people how to rip Switch games".

The problem is that a DMCA 1201 compliant Switch emulator would be nearly useless. To be clear, the legal way to use the emulator on your own purchased games would be entirely undocumented. You probably couldn't even say "figure out how to rip the games yourself". The illegal way to use the emulator - i.e. with pre-decrypted, pirated game files that don't rely on any Nintendo keys - would be very easy. But they can't tell you to do that, that would be inducement.

Homebrew developers could still legally release their own games for use in a Switch emulator. And emulator developers could advertise the use of the emulator with those games. But that's really limited and I could see Nintendo convincing a court to just ignore it.

[0] e.g. Sony v. Connectix