This may be out of the reach of many older Tesla cars, and it's not certain if you'll get to either speak directly to people outside or send automated speech (say, to warn that you're backing up). It could still be helpful both for convenience and as a safety measure, though. You could alert an inattentive pedestrian without taking the time to open your window, or deter a would-be intruder without either honking your horn or exposing yourself to added danger. And given what Musk said, we wouldn't be surprised if you could use this to make people giggle as you roll past.

Teslas will soon talk to people if you want. This is real. pic.twitter.com/8AJdERX5qa — Buff Mage (@elonmusk) January 12, 2020