Hi!
Recently I read the thread about forensic companies trying to get into Pixels with GrapheneOS.
I think there is also another threat - no protection from an attacker when the screen is unlocked. Of course this is nothing new.
But having a system service that requires to enter a password every given time e.g. 15 or 30 minutes would add significant protection. It could show a notification 1 minute before locking the screen to ask for the password. The feature would of course be opt-in, only for users that need it.
Benefits:
Someone taking an unlocked phone from your hand most of the time is not a trained intelligence agency person that will immediately start to extract data from the phone into a USB stick. So the protection would be useful in most cases.
Even a trained person is still a human who can make mistakes. So having a 15 minutes countdown could be useful against such person as well and could protect the data on the phone.