What if it was announced that you needed NSO to even play Sword/Shield.
How would you react?
It personally would be a deal breaker for me, and would make me furious that I missed out what could be the best Pokemon games yet because Nintendo wants to push their online service.
Not going to happen. It'd be likely necessary to do trading and battling via wifi, but for just playing the game and doing the story, catching, etc? I can't ever see that requiring the online connection. That'd especially go against quotes of the game being more handheld focused than LGPE (ergo, when people wouldn't be using the internet at home).
I expect local wifi trades/battles to be possible once again.