Here's my pet idea for a hardware product I'd totally use:
A Google Glass like device without most of the functionality (no camera or mics) or processing hardware (doesn't have to run its own OS), except the display (this should cut down costs quite a bit and make it a bit more feasible to manufacturer and purchase than Google Glass itself).
You connect devices to it using Miracast and/or some other wireless display tech and extend/mirror your smartphone/laptop displays.
It can serve as a portable multi-monitor setup for productivity, or a simple portable heads-up display for entertainment (video playback, reading) or utility uses (navigation).
That'd be the MVP anyways. In future revisions you can maybe add things like a mic and/or camera for things like augmented reality and voice control, but figure out how to offload the processing to the master device (laptop/smartphone) rather than dedicating hardware to it on the device itself for affordability and battery life.