If it becomes cheap enough then most smartphones will have it, no doubt, if only to fill the checkbox. I stronly doubt it will become a feature absolutely necessary to compete within the next few years, though. To me it seems more like the presence (or absence) of a physical keyboard - some people will require it, some won't.Of course I'm not expecting stereo 3D to become a requirement in OSs in the next 2 years. Rather that no high end smartphone will ever be able to compete if it doesn't sport that feature (with lower-ends following that same trend in the following years).
Something like having a 3.5" screen today. No sub-$450 smartphone has a screen smaller than that, AFAIK.
Don't forget that using a parallax barrier comes with a power and resolution impact.
I suppose you meant "above $450".