That's fair, this would still be a valuable development even if Motorola doesn't end up shipping devices with GrapheneOS preinstalled, but if they did I think there's a lot of potential for them to enter the mainstream. A device with GrapheneOS without any [major] caveats (like Play Integrity API, Google Pay not working) would be a game changer.

I can't see such a GrapheneOS existing without explicit Google support. And I don't think Google would support something like that unless they suddenly decided to actually not be evil again.