Vaping will never be allowed in movie theaters, if for no other reason, because some idiot will try to fog up the room. You are not suppose to use your cell phone or talk at the movie, not because of danger, but because it is rude. If you are doing something without others even noticing, who cares, it is your business.
I do have a problem with the comment above where there seems to be a sentiment that we need to ensure "vaping poses no danger". I can't think of a single thing I do all day that causes no danger. Driving (crashing, carbon monoxide), standing in the parking lot (carbon monoxide/allergies, bees/insects), typing on this computer (radiation/carpal tunnel), drinking my diet soda, etc. The fact is, it hasn't be shown to cause any danger. I don't want to live in a world where we are banned from doing things that haven't be proven to pose no danger. If you don't do these things, then you will never know if they pose any danger. Heck most medicines out there have been proven to pose a danger, often MANY, MANY dangers including DEATH.
Things should only be banned when they are shown to cause a more danger than benefit that they deliver. If we don't follow this model, we would never have automobiles...