I think the subscriber rate for GP is pretty high among Xbox owners since you have to have a sub to play online games. I wouldn’t be surprised if more folk have GP subs than PS+ ones.The era of New Console, and New Games specific to new Console with distinct generations between is over.
Looking at Gamepass now, it's everything from original XBox games, through to Series X optimised. Companies are still releasing new games for Xbone.
The reason to buy the new console, is because you're in the market for a console, and the "new" one is the one Microsoft is selling now. Xbox is a subsidised, turnkey gaming PC, and just like your next gaming PC is just a better specced version of your old gaming PC, that's what (microsoft's) consoles are evolving into.
"Generations" are done, just like "console wars".
If you don't buy a console, but keep using Gamepass on your existing console, you're probably a more profitble customer for Microsoft, than someone who buys every console, but never subscribes.
I am also curious if MS could move away from X86 (in a new console) and still maintain backwards compatibility.