GrapheneOS community manager here. The problem with something like this is that it cannot be reasonably hidden when it would be exposed by someone using basic tools. Our Duress PIN/Password feature doesn't make any attempts to mask itself, precisely because we think doing that only gives people a false sense of security.
We think there's a good chance a motivated adversary is going to be familiar with GrapheneOS and its features, and the more mainstream it becomes, the more this can mean "your abusive significant other" rather than someone at the border.
The moment people know this feature exists, it can become dangerous even if you don't use it. You can be threatened to unlock, and even if you do, the adversary can choose to not believe you since they can think you're just hiding it. That puts you in a dangerous situation where they think you can provide something that's literally not there.
It's a very difficult problem to solve, and we don't think that proposal can solve it.
We think there's a good chance a motivated adversary is going to be familiar with GrapheneOS and its features, and the more mainstream it becomes, the more this can mean "your abusive significant other" rather than someone at the border.
The moment people know this feature exists, it can become dangerous even if you don't use it. You can be threatened to unlock, and even if you do, the adversary can choose to not believe you since they can think you're just hiding it. That puts you in a dangerous situation where they think you can provide something that's literally not there.
It's a very difficult problem to solve, and we don't think that proposal can solve it.