The biggest boon might well be to regional theaters in niche markets. Demographics can dramatically alter the tastes of an audience, and the current model of film-distribution is a poor fit for theaters in an America whose population is increasingly migratory and shifting. A neighborhood that had been (for example) predominantly middle-class African American for generations can become an enclave for immigrant families from Russia within a generation given the right set of economic circumstances, and a change in consumer-base like that can cripple some businesses and embolden others. A movie theater that could stream, say, Bollywood movies because they've noticed more folks of Indian descent living locally - better serving their communities in real-time without having to wait for Hollywood to catch on.
YOU WILL NO LONGER BE ASKED TO TURN OFF YOUR PHONE
Here, then, are two undeniable truisms:
1. The devices will still be called "phones," even though they are more accurately small multipurpose computers that can be used as phones, among other functions. They are now integral parts of modern life for more and more people, and that is not going to change course any time soon.
2. It is incredibly annoying when people talk, text or otherwise make use of their phones during movies. It's rude, and you shouldn't do it.
But... well, back to Number One: People feel, fairly or not, that their lives increasingly depend on having constant access to this or that information via their phones already - how will they feel when these devices are (very soon) also heart-rate monitors or medication reminders? What will we do about phones in theaters when it really, finally is widely considered an undue burden to ask that we turn them off? Other than bemoan that we somehow let ourselves get to that point, I mean.
Well, for starters, someone will have to invent a way for things like texting or whatnot to be functional in the dark, or at least dark enough to not be obtrusive to others in the theater. Don't ask me what it'd be - some kind of haptic-feedback addition to the touchscreen, a version of Braille for the otherwise-sighted perhaps? Or maybe it's possible that a variation on the technology that can make laptop screens only visible from a specific angle could be used to render smartphone screens nice and dim to all but their immediate user? Whatever. Point is, like it or not someone is going to work out a way for people to text their pals and check their stocks during movies without unnecessarily intruding on other people's experience. Worst case scenario, we all just accept that a sea of glowy squares in otherwise-dark theaters is just the new reality. Active mini-computers will be common accessories in theaters... and that's potentially exciting to me.
People are already using smartphones to play MP3s of commentaries for newly-released movies ala RiffTrax (using headphones, of course), so why not apply that idea to other areas in a more official capacity? You could, theoretically, listen to a movie translated into a language you're more familiar with than the one it was produced in. Alternate soundtracks could also be used to loosen the MPAA censorship requirements for "strong language" - an adult could listen to an "unrated" audio stream while a "cleaner" version played over theater speakers.
And speaking of features like that...