That feature is right on the border between real neat tech and deeply unsettling.
"Hey, my phone uses its last few electrons to turn into a bluetooth beacon to stay findable" sounds like sci-fi "reserve power emergency mode"
"I can't turn off the locator chip in a device that holds half my life and memories" is just dystopian.
I'm wondering if there would be a way to keep it useful while minimizing impact for people who stay off the grid. A hardware switch would probably be a good start but they won't fly with current all-touch designs.
It will be seen how they implement it, but since Google is creating their own version of the Find My network, it will likely be tied to activating that. If it’s anything like the way the iPhone does it, disabling Find My would turn it off, they might (should) also provide the option to turn it off when powering down your phone.
minimizing impact for people who stay off the grid
People who stay off the grid don't have smartphones!
As much as we enthusiasts like to try and have our cake and eat it too, the only way to really be completely private/secure/anonymous is to be completely disconnected. Threat models and compromises and all that.