I suspect that the tiny amount of power you can vampire to make NFC work (which is why your contactless bank cards work as you explained) isn't enough for even the basic features we now expect from a smart phone as payment device.
So you'd have to message this very carefully, on top of the engineering effort, and my guess is that in reality "Reserve power" is always enough. If your phone "died" (screen turned off for lack of power) at the party, you have several hours after that when it can still do enough NFC to get on the bus home.
A lot of my friends get anxious at like 10%. Sure, at that point you should probably stop playing Candy Crush, but you're a long way from not being able to tap in to your train home if you stop. Power Reserve seems like a sensible choice to make you stop using the last dregs for frivolities.
We might see this again, as the Pixel 8 Pro has a system like this for UWB so your phone can be located by the Find My Device network after its power is drained.
So you'd have to message this very carefully, on top of the engineering effort, and my guess is that in reality "Reserve power" is always enough. If your phone "died" (screen turned off for lack of power) at the party, you have several hours after that when it can still do enough NFC to get on the bus home.
A lot of my friends get anxious at like 10%. Sure, at that point you should probably stop playing Candy Crush, but you're a long way from not being able to tap in to your train home if you stop. Power Reserve seems like a sensible choice to make you stop using the last dregs for frivolities.