I want a voice control experience that is functional. I don't want every bad thing that could happen-- especially those that will only happen if I'm careless to begin with-- circumscribing an ever shrinking range, often justified by contrived examples and/or for things much more easily accomplished through other methods.

Probably need VoiceID so only authorized people can talk to it.

Oh no, what if they put on Christmas music playlist in February? the horror!

There should exist something between "don't allow anything without unlocking phone first" and "leave the phone unlocked for anyone to access", like "allow certain voice commands to be available to anyone even with phone locked"

Not really. Giving the weather forecast or playing music seems pretty low risk to me.