How would this work? Could there be a cooldown period? e.g. commits sit a day before being auto-committed?

Validate really only validates Linux x86_64. The situation is already quite dire for other architectures and OSes,

I fear making it worse by not allowing people time to object.

Would this be a per person setting? This just raises so many questions. And I don't quite see what problem it's solving

because presumably code is tested before it's put on Phab isn't it?