I think that's extreme obviously. Gamepass has always had the potential to experience exponential growth. The amount you get for the money is pretty much unrivaled. If MS studios are in a regular release rhythm over the next decade along with Call of Duty on it, it's not like it's impossible.
Is it likely? No, not really. But if for some reason it finally caught on it's available nearly ubiquitously and would be easy to pick up for people if they want, on PC, phones, TVs, browsers, console, and maybe a handheld coming up. I mean Disney+ is complete shit and that somehow has 149 million, and 10 years is a long time.
It really just comes down to consumers actually deciding they want it in large numbers. It's possible but we really haven't seen that yet. Even 100 million would be shocking at this point. I think they may have a shot at substantial growth when Call of Duty hits the service if they actually invest in substantial, expensive mainstream advertising for like 2 years.