As far as I understand, broad device support is a non-goal for the GrapheneOS project. They are striving for decent security/privacy rather than wanting to attach their name and resources to mediocre standards.

I believe nothing prevents other individuals and organisations from building what you're suggesting with GrapheneOS code and ideas.

I would argue that "works fine" != "direct support" when discussing vendors and platforms. Support is a commitment signal, not just a technical capability.