These people are a pox on public transport.
I also use the phone's internal speakers for playing the notification sound. (And, technically, ringing.) I sure hope that's not going away.
Quite frequently found at highway truck stops, though almost certainly other electronics stores as well.
Wireless is convenient.
Wired is reliable.
YMMV.
Bluetooth's more reliable than USB in a car anyway.
Maybe I'm in the minority but I could never imagine not having music pumping in my ears.
I dont want to charger yet another device in my daily routine. I won't, actually, and will steer away from any phone that requires active headphones to work.
I'm not saying I agree with getting rid of the headphone jack. The amount of utility it provides is pretty high relative to the volume it takes up.
Yes, as you say, by moving the power draw for the DAC to another device, which must be charged separately. This isn't a real gain in battery life in any way.