* "Me mode" that unlocks everything.
* "Kid mode" that only allows one's kid access to pre-approved apps and features.
* A "lend to a stranger to make a call" mode that is a lot like the kid mode, but it also causes the phone to start broadcasting its GPS location frequently (and refuse to turn off [though it might fake it]) in case the stranger steals it.
* An "under duress" alternate PIN that unlocks an alternate profile full of nothing but benign activity, with no indication of (or access to) the encrypted real profile. Once in this mode, the phone cannot unlock normally without a non-phone 2-factor authentication (e.g., email).
All but the last could use the normal PIN, perhaps with different "submit" buttons. I would also love to see the same thing on ATMs, where an alternate "I'm being robbed" PIN will show a fake, low balance in the account and limit withdrawal to that value.
Applying it to phones seems a bit unrealistic, given that so few people will actually use those features.