Then why make a console at all?
Where else are they going to push GamePass? Nintendo doesn't have the hardware to run many of the GamePass games and remember how much Sony hated EA Access until years later they finally caved in? No way would Sony want the GamePass service on their platform, it would make PS Now pretty pointless unless they too started putting their games on there day one.
Releasing a console gives them a place to push the service and make a lot more money than they would elsewhere.
The Switch probably can, if all their 1st party games are designed to scale and run in 4k/60 or 120fps on Series X.
This is exactly what I've been saying for months. GP is fantastic but it gets in the away of launching a next gen console and pushing its hardware. Series X doesn't have exclusives because MS doesn't want games on GP that are designed around high-end specs. I mean how great would GP be if your pc couldn't run 95% of the games on there? Almost every pc on the planet has access to GP, so that's obviously where MS expects to get most of their revenue from in the foreseeable future. Their end game is Xcloud, though, so they can go after the mobile gamers and have GP pre-installed on Samsung Tv's.
MS is thinking about potentially reaching 2 billion people, so why would they care about a max Series X installbase of like 50m? I'm Pretty sure they would have to pay royalties to companies like Samsung as well. So when you think about it, it wouldn't make business sense NOT to release GP on ps5 or Switch.