I'm not sure we'll ever see this on a Mac, but a 2013 BBC article saw TED fellow Jinha Lee predicting transparent computers will come into general use within a decade.
Lee works on Microsoft’s SpaceTop 3D system, which consists of a transparent LED display with built-in cameras that track the user's gestures and eye movements. It consists of a clear-glass display that allows input using voice control, touchless motions and eye-tracking.
You place your hands behind the screen to scroll or type just as you would with a regular computer. However, you can also raise your hands up to grab and manipulate the virtual 3D elements.
One camera is used to track fingers, recognizing gestures like pinching and dragging. A second camera faces the user and tracks the position of their head to display perspective-corrected 3D graphics.
Among other things, you'll be able to check your e-mail from a clear glass structure, just by waving your hand or post pictures on Facebook using a voice command. Or use your eyes to motion for the computer to turn off.
Then there’s the “BigScreen” concept, virtual desktop that lets you use your entire computer desktop, with anyone, in virtual reality. In theory, anything that you can do on your computer – browsing the web, watching videos, playing video games, and even productive work – you can do in VR on massive screens with BigScreen.”
Basically, the idea is that you wouldn't even need a monitor; you wear a VR headset and you "see" screens. This is also something that Oculus is pushing (but useless for Mac owners, of course), but can you imagine a future 35-inch iMac with no physical display? (Or could it be an iMac if it has no display? Hmmmm.) It would be really light, and probably quite a bit less expensive. Of course, it needs an Apple VR headset first.
The idea of a transparent Mac isn't new. In 2006 MacFormat magazine ran a "Macs of Tomorrow" section with an illustration by 3D artist Adam Benton that's one of the coolest mock-ups I've ever seen. Pictured, it's a full wireless Mac with a LCD screen that's transparent when it's not being used. The transparent keyboard also sports light sensitive illuminated keys. And, I'm sure the display is touch sensitive.