This can't be a new thing. This was one of the conditions Nintendo announced when they dropped their stupid "register with us to be allowed to do lets plays" thing.
Oh, and it's not just Nintendo. All of the big publishers believe they own your videos that use their games. I've been involved in discussions with people personally who were trying to figure out how to demand licensing fees from YouTubers.
This is goingnto get worse before it gets better. This has been a traffic jam caused by everyone waiting for somebody to go first. Nintendo is just the one who has volunteered to be the first mover.
This is not about the legality of emulation, unfortunately, but about whether people have the rights to publish lets plays without a license.
Many suits in the gaming industry see lets plays as theft. They see people making money using their games and believe lets players should have to pay to license thst content, and that they should have the right to revoke that license if they don't like what people are saying about or doimg with their games.
I work in the industry, and I know people who work or who have worked at studios owned by every major punlisher in the west. This is a thing they all habe someone of import chomping at the bit for.
It's just that none of them want to be the one singled out as the first or only one attacking lets plays. Nor to be the one that shoulders the costs of having their position challenged in court.