For PS Now, if they run on PS4 hardware (like the PS2 ports which run native) then it's downloadable. Anything else (PS3, PS1, etc) is some Stadia bullshit.
I still don't see them throwing the cash around to secure major third parties the way Microsoft has - PS Now isn't central to their business strategy. Game Pass has completely changed how people use their Xbox.
They said every month, they will add a handful of "marquee" titles that will only be around for three months, if the initial batch is anything to go by. This is in addition to the "evergreen" titles that stay on the service for roughly a year. I expect the marquee titles to be on par with Game Pass games, and there's a huge library of Japanese games to draw from that aren't available on Xbox at all.
This PS Now news is even better than it appears initially because you don't need PS+ to play any of the games in PS Now online. You would need XBL Gold or Game Pass Ultimate to do that on Xbox, whereas PS Now is as low as $5/month if you do the annual plan. (You can wait for one of the $15 back when you spend $100 promotions to save a little more money.)
The last benefit to PS Now that shouldn't be overlooked is that cloud saves stay up indefinitely. So we all know cloud saves are free on Xbox One, but it's paywalled on PS4, PS3, and Xbox 360. PS Now circumvents that.