Proof of Concept - See through OLED screen on a laptop
gizmodo.com
gizmodo.com
Those low resolution IR cameras must have been produced in such huge quantities I bet they are pretty cheap now. You can buy a Wii-mote for $50 retail and that includes lots of expensive hardware you don't need such as a bluetooth transceiver and a pair of accelerometers.
Check out his entire youtube channel, it is full of interesting software/hardware hacks.
For this to really be feasible for everyday tech, it would need to be married with something to detect these clashes and adjust opacity/colorschemes appropriately. Similar (in concept) to those eye glasses that darken/lighten with the amount of ambient/direct light (maybe just sunlight, I never had an actual pair of those glasses) that you encounter.
Update: This also says nothing of how this tech will react to direct sunlight. In direct sunlight, how will something like this compare to a tech like full color e-Ink (or even just black/white e-Ink)?
This could be the same resolution as the OLED leading to some funky transparent pixels and some not.
Possibly also oscillating to create semi-transparency (and perhaps seizures :( )
I'd be more worried about the front imagery obscuring what's in the background, in case people start putting this on car windshields or sunglasses (i'm speculating but hey, we're talking about future anyways).
It's much cheaper currently to project onto a mesh film for close to the same effect.