Remember when some movies used to have intermissions (stage plays still do) with a nice 10-15 minute bathroom break for the audience and to restock on concessions if needed, plus allowing them to dwell upon what they just saw.
I think it could honestly work well with extremely long movies that end up around 2-3 hours long (any shorter and there really shouldn't be).
Because honestly there are so many times in long movies I am sitting there needing to pee really bad but by the time I have to pee it's at least an hour and a half or more into the movie and that's where most movies really pick up their pace. Plus there are tons of theaters that do 'Free refills on larges' and while 99% of the time I never need a refill (only time I did was when I was sharing a large with a bunch of people, heck I never get larges unless I am sharing with lots of people) and when I do, nobody wants to get up and miss out on the movie (unless it completely blows, which then I probably would just flat out leave) to go get more concessions.
I think it would be fairly productive and while it adds 10-15 minutes to an already long movie, it adds a lot of convenience to it, plus everybody at some point has experienced going into a long movie and sitting there needing to pee badly but cant because they don't want to miss anything.
It would work really well in my opinion and most movies could use a nice break point to leave the audience in added suspense after a big plot twist.