using such a self-destruct mode would be a certain way getting yourself charged with destroying evidence/contempt of court/... though.

This would be difficult to prove. They would have to know for certain the evidence was on there to begin with. I don't see the prosecutor easily meeting their burden of proof on this charge.

This is how the statute is worded here in Illinois:

"A person obstructs justice when, with intent to prevent the apprehension or obstruct the prosecution or defense of any person, he or she knowingly commits any of the following acts: (1) Destroys, alters, conceals or disguises physical evidence."

Ugh. It's a vague law. I don't even know how they would prosecute that for virtual evidence held on a device that they didn't already have a view inside of.

i was under such duress that i was shaking so badly that i made typos in my 30 character password 10 times. the loss of evidence is not my fault as it is the people putting me under that duress. don't think it'll hold up though

No 5th Amendment protection? If you spoke the command / "password", would it matter?

FaceID can already prevent a device from unlocking if someone is sleeping. In theory devices could detect if they were being unlocked "under duress" by using biometrics to look at facial expressions, heartbeat, etc, and then wipe themselves. I don't know how practical in reality but perhaps it could be a feature you turn on in a sensitive environment.