In a previous life, I spent a lot of time hang gliding. Competition and Cross-Country pilots have to hang multiple instruments on their control bars - variometers, GPS's, radios - to maximize their performance. This is a problem area, as the $1000 worth of instruments are in an easily damaged location which also reduces performance due to air drag.
Google Glass would be a huge advancement here - stick your $200 cell phone where it gets good reception and is protected, use it for GPS, mapping, and communications functions, add a small cheap variometer interfaced to your phone. You'll have far better information, your instruments will be cheaper and your software will be vastly better, and your physical performance will improve by taking all that stuff out of the airstream.
This, I think, is an example of the niche markets that no marketer in his right mind would build a product to meet, but combined with 1000 other niches could start to make the product ubiquitous. /frank