I'm halfway on this. I think that 3D as it stands is a fad, because it has the inconvencience of being basically unwatchable to people with really bad eyesight who don't wear contact lenses, and even if you have the eyesight you have to wear those silly little plastic 3D glasses, which are ridiculous and can get in the way of the enjoyment of a movie ('One size fits all' my British arse Vue cinema)
BUT
I do think that if there can be any way to make things appear 3D without needing those glasses then I think it would very quickly become the norm. Of course, this might only be possible with the invention of Star Trek like holograms, which I'm not sure would actually constitute 3D.
So basically I think entertainment in 3 dimensions is the next step, but not with the technology we have now. (Assuming of course that the ultimate goal of entertainmet technology is to make you feel like you're in the middle of the action, virtual reality, then 3D must be a step on that road.)