Some time ago i say something similar in another topic.
I even started look for hardware to do this "trinket" my intention is buy a model A specifically to do one. my auto imposed deadline is in july/august(if possible in time to FISL rs) , my intention is mounting inside a Headset with large earphones in one site the Rpi in anothe the batteries and auxiliary hardware(gps, gsensors, webcam...), a adapted keyboard in the forearm.
The first prototype will be a very creepy thing since everting will be improvised, but to the follers versions(hopefully the third untill the end of the year).
The intentions to software/hardware integrations includ sensors to hand movement(instead mouse) augmented reality using gps+Gsensors(kind a map or turistic information about the region tha you are)
With the Gsensors will even is possible caths the possition were you are looking an add some extras in this.
In the first problaby i will using a 1,5"LCD from a foto frame or a cheep chinese mp4. in only one eye using a Fresnel lens(this will be harsh to find) due the proximity whit the eyes.
My intenions include post the steps in some blog, and obviously here in the forum.
excuse my bad english i'm from Brazil