I don't think Microsoft, even despite what they say publically, is that interested in having Game Pass on Playstation in particular.
Now that the game division has the green light from the higher ups to spend big money on acquisitions like Bethesda, I don't think for the immediate future they really have as much interest on putting content on Playstation devices, not as much as people think.
They're going to leverage Game Pass to get more people to buy more XBox hardware.
With regards to Nintendo, I think Nintendo will eventually just work with Ubitus and most big ticket 3rd party games being available to play on Switch will become fairly common that way, and I think Nintendo is fine with that. They get their license fee cut and don't have to share.