An employee at a large frame company (wont specify the brand) told me that the cost of materials for their $2K+ composite frame is actually less than $20. The consumer, apparently, pays for their R & D, and their labor costs, but not materials cost.
So all you'd have to do is move manufacture overseas and there you have it, cheap plastic frames.
We'll see more of them. (note, we're talking about composite frames, not necessarily carbon fiber)