SX OS is certainly illegal in US and UK, the same as DS flash cartswere.
An emulator for what? If we say that DeCSS emulates a DVD player, then that is illegal in the US. The case that most people go back to for emulation being legal is Sony v Connectix, but that was before DMCA & Connectix didn't need to bypass any DRM.
Nintendo are a bit slow off the mark with SX OS, they used to have customs officers seizing DS flash carts and sued many sellers (who tried the homebrew angle and failed). I suspect they realized that no matter how much money they spent on shutting them down, it made little difference to the amount of flashcarts on sale.
It's probably more effective for them to let people spend money on SX OS and then invest in finding ways to ban them or mess with them in other ways. That way people can end up regretting buying SX OS and won't tell their friends how great it is.
Emulators in general are legal to download. Just about every single core in retroarch has a standalone emulator which they are based on, all are legal to download.
To play devils advocate, lets say YUZU though. Downloading YUZU is not illegal, it can only play dumps of switch games. Most people that download it in the US are without a doubt using it for piracy.
Yet you can argue its intended purpose is to play legally owned backups of games, that youve personally created.
If YUZU can be deemed legal, how can you argue SX OS is illegal? SX OS provides other services aswell for which no DMCA case can be made.
Basically if you want to say SX OS is illegal you have to argue that its intended purpose is to circumvent copyright protection. SX OS will argue that it isnt, and because you can use game backups legally considering you own them, their lies the flaw.
You cannot state as a fact what SX OS’s intended purpose is, so you cannot claim gospel truth that their OS breaks the law. It is really that simple.
Certainly downloading YUZU, gives a much easier means of piracy, with a much more direct path, and no other option than to play switch backups.
Yet that is considered legal.
Like I said find me 1 article that specifically says
“SX OS is illegal”, even from a shoddy website I honestly dont care. When you do, you will have a much more solid case. Banning their products in certain countries is not the same thing. Nor is shutting down a few ISPs when 90% of the attempts in other countries failed. Nintendo certainly care, the problem is the laws are too vague.
You want to claim they are illegal, then provide 100% proof of which law they are breaking. Just saying it means very little. If a case can be made for YUZU, it certainly isnt the DMCA.