It'd seem to me that, with an integrated design (ie, one not tied to existing display hardware) that you could get the effect of a very large screen with a tiny display and an optical system generating a virtual image.

How sharp would the initial resolution need to be to ensure image crispness in the virtual image? Like blowing up an old-style photograph, I'd guess blurriness would become an issue very quickly. That might be one reason this technology hasn't popped up yet.