That much-vaunted "retina display" on Apple's new iPad is pretty fancy, but at nearly 10 inches diagonal and weighing 1.5 pounds, you have to deal with a huge piece of hardware. Instead, wouldn't you rather have a display with the same number of pixels in less than an inch of space? Sure you would!
You're probably thinking that hell no, you wouldn't want an iPad an inch wide. You'd have to put it right up to your eyeball to see anything! And that's exactly the idea with Fourth Dimension's microdisplay: it's for virtual reality. I know, I know, virtual reality is terrible right now, but displays like this are going to change that. Small size and high resolution means that you can make mobile electronics that are comfortable to wear but still provide VR images with "retina display" levels of realism. And with some of those contact lens eye upgrades, you'd be able to sneak these displays into sunglasses.
Eventually, Fourth Dimension is hoping to work their micro-QXGA displays into some sort of gaming peripheral with an integrated head tracking system. It's in talks with a number of "high-end" companies to develop a producing in the $1,000 to $2,000 range, which'll likely only appeal to people with a serious gaming problem, at least at first. The thing about VR, though, is that so many companies have done a terrible half-assed job with trying to make it cheap as opposed to good, that there's still a market there of people (myself included) who would totally buy something like this as long as we could put it on and be absolutely blown away.