Yeah the title of this thread had me thinking that Nintendo was somehow banning people for using any used switch carts at all. That would have been far too much of a greedy money grab.
This is smaller and ok with me if true. Banning people who are using dumped/flash carts in multiple places simultaneously, and that happens to catch the original dumped cart, that's ok with me. Don't share your dumped game with others who are not you, and you are fine.
Theoretically we are only using flash carts to backup and play our own owned games is all, not passing that around. Nintendo is now just keeping us extra honest.
Even if I dump my cart to a flash cart backed up to a PC and my original cart gets blended, I still have my clean backup copy of my game I bought for myself on the flash cart.
So I'm ok with this. It makes physical carts into license keys just like windows keys or digital game serials, but better because you can copy the entire cartridge, not just a serial key to give you a permission slip to download a copy of a game from some server they are counting down the days to turn off.
Signed , someone who just had to ask his boss if he could keep one of those servers on a while longer (not for games but same basic idea, the resources were to be downloaded from 'somewhere' and I run the somewhere)...boss said yes. In 5 years? I'm not sure he will says yes again...or if I will be the guy asking.
So dump those physical carts you paid for. But don't share em. Else you risk this...seems fair to me.