This is something I've anticipated and pondered for a few years now, and I think it parallels what has happened with Hi-Fi over the last couple decades. For most of my life I have been an early adopter. At college I was one of two kids in the entire residence hall that had a CD player. Later on I was the first person I knew that had a CD burner. It's funny- early on no one believed me when I said I burned my own discs!

But early on I saw that technology as an existential threat to recorded CDs (this before most folks I knew were online). We all know how that story has unfolded. The same digital technology that brought us high resolution SACD & DVD-A recordings also brought lossy but tiny files that could be moved even over the pokey dial-up internet of the day. We stood at a crossroads; extremely high quality or supreme convenience. Although both exist side by side to a degree I think it's fair to say that convenience has won out. MP3 won the race to the bottom and it took Hi-Fi with it. True, there's still a high end and lots of great makers (especially the smaller ones) but overall it's a niche product, a fetish almost. I know virtually no one under 25 that is into "stereo" (a blanket term that covers the playback of high quality recordings through good equipment).
Will movies follow the same path? I'm closer to 50 than 40 so maybe I don't have my finger on the pulse of movie industry anymore. In years past I always had a projector but when my last one crapped out I didn't replace it. LCD/LED sets have gotten big enough that to me it's about a wash. Maybe someday I'll go back to projection but due to lifestyle concerns I have transitioned to a flatscreen. I've never been to a theater that could hold a candle to my home system sound-wise, but I find myself going to the theater almost every week for the big screen. It's more than that of course; I like getting out of the house and seeing it on the big screen. At home there are distractions but at the theater I'm focused just on the film.
But what if all the films were available day-and-date at home in a streaming format? That's a lot tougher! My TV still isn't as big (in terms of degrees of field of vision) and the theater. But I have to admit it would be nice to never have to worry about morons chattering away or flashing me with their cell phone screens. And pausing if for bathroom breaks would be nice.

What does this mean for theaters? I honestly don't know. Parents will have date nights at the theater as an excuse to ditch the kids. Some folks will always want to see a big screen. Some folks have no theater system and value the experience of the XD or IMAX theater.
On the other hand I know people that watch movies and TV on their cell phone by choice.

For them the race to the bottom is finished.
If we lose brick-and-mortar theaters what does that mean for movies? Again, I dunno. Certainly watching a film would be a very different experience than I have been used to. After all I saw the original
Star Wars at a drive in theater! When I was a kid you could watch a movie at a theater or wait for a heavily edited version to hit TV a year later. No on-demand, no option to see it again in a year, no streaming and not even videotape until I was in my teens. But maybe the experience I grew up with isn't the norm for most people anyway.