It doesn’t matter if it’s emulated legally or not. They can issue a takedown for showing gameplay captured from an NES hooked up to a CRT if they want.

A fair use defense has to be defended in court, and it’s not just about whether you’re right but also about whether you can afford to fight.

It’s also not certain that a fair use defense would fly. One of the elements for determining whether fair use is market impact, and I suspect that Nintendo’s lawyers would argue that demoing that their games can be emulated - even if the specific demoed games are not being sold - has a negative market impact, since it makes people who might buy a Switch and a Nintendo Online membership to play the official emulated games less likely to do so.