My understanding (And I could be wrong) is that BOTH frames are simultaneously transmitted. With both lenses showing the same thing you'd not get any strobing or framerate drop, just only half the potential picture. Since effectively for the stereoscopic effect, both eyes need to see a full picture with an offset, you'd be seeing the same as if you'd watched the picture in a 2D cinema.

Unfortunately I don't see it going away any time soon.Some movies have used it badly. Some have used it amazingly well.