I've been thinking about this for a couple days now. I must say, if this is true, it's probably the biggest industry news since MS announced their entry into gaming. It would be absolutely massive for Nintendo and MS, obviously. But, it is nearly certain that Sony would do something to either counter, or jump on board. PS Now would work on Switch the same as Gamepass, with the same benefits to both Sony and Ninty. But, really Gamepass on PS might be a possibility too.
The benefits for MS are obvious there. But, I see a big benefit for PS as well. If one can play Forza, Gears, and Halo on PS, there is really no reason left to buy an XB console. That would effectively leave PS as the only real player in the home console space. MS gets their GaaS money, Sony gets rid of their main competitor in hardware. Gamers get all the games from both. Win-win-win.
Sony could also put PS Now on other devices. That's probably a more likely scenario. But, it doesn't have the same Earth shattering implications. So, it's not as fun to BS about in this forum....
No, the one that would benefit the most in your scenario would be Nintendo, because if you owned a Switch, you would have acess to basically all games that ends up being released.And that would be a dumb move for Sony, because that would undermine their console, since you know, the Switch is also a home console.