Well it does have some things yet to be developed further, even though you are correct there that some models are very pocketable.

A projector is not optimal display device when commuting in a train or bus for example, it needs some kind of flat surface to project on, and to be usable you need to mount it somewhere. (holding projector in one hand and surface in the other is a no-no)

What I consider the killer application is equivalent of a newspaper; it should be easily foldable/rollable, be durable and have good contrast ratio and high enough resolution to be used anywhere.
Plusses for reasonable environmental protection and low energy consumption.