Xbox is officially Xbox hardware, PC and mobile. aka multiplatform. Now that the obvious is out of the way, let us talk about GamePass and Xbox Game Studios possible projection. Xbox Game Studios has purchased a new studio every year since 2018 with last year being the exception since the deal for Zenimax only closed this year at ~7 billion dollars.
The average production schedule for a triple A game is around five years. This enables Xbox Game Studios to eventually reach a point in which they can effectively release 4-5 triple A games every year with just its in house studios. Depending on the timeline, that successive flow of games can be either this year or next year but once it has started, they can effectively maintain that momentum indefinitely. Which I believe is there strategy for validating GamePass even more over time.
Just for some perspective, Netflix spent 17+ billion dollars in content just in 2020.