GrapheneOS is interested. That said, there might be a reason why Google hasn't enabled it yet.
That reason might be because they want to enable it when they have improved/finished their desktop mode, or it might be that it is buggy and can cause serious issues, so they're keeping it disabled until those are addressed.
For GrapheneOS to enable it early, rigorous testing would need to be done to ensure that it is safe to deploy at this time.