It'll probably start with 2d -> 3d because a lot of work has already been put into tools to automatically take images and convert them to 3d. Ultimately direct to 3d will work better, but we will probably need more 3d data for it to reach it's potential, so 2d -> 3d might last for a while. In the interim, people will do all sorts of hacks on top of 2d -> 3d to reduce the amount of required human intervention.