I do realize that some scenarios where bio fails exist. But I don't want simultaneous security all the time, I want an option to enable it and disable it when I want. E.g. I'm traveling through customs and I enable this mode - now the phone can't be opened by e.g. restraining me (or tricking me) and using only bio, they won't know the password to match. And if they will request to unlock my phone for inspection, well ok - but they can only look into it beside me, the minute it autolocks they won't be able to open it knowing only password that I provided because my bio is inseparable from me. Some other valid scenarios can also exist.
PS: I read that some community firmware images allow this mode, the only thing that stops me from using them is lack of camera drivers for unofficial firmware.