Mobile networks are moving towards IPv6 now, so phones are uniquely addressable again. Making them reachable from outside (if they aren’t already) is a trivial problem to solve should there be demand for it.

But I don’t see any major use-case for that - the main issue of battery life remains for any significant usage, and frankly I wouldn’t want to have something running in the background that would deplete my battery in an hour because someone happened to connect and watch a video hosted on it.