1) Radios. The newest versions of Bluetooth on the drawing board are supposed to run at 24 megabits a second. 2) Batteries, the same way glasses with wearable cameras work now. The added bulk of a portable generator to charge it and associated equipment would be awkward, for much the same reason your phone doesn't come with a hand dynamo. Or.. 1) Wires. It's no serious hardship to run a wire behind the ear from glasses to a small device. 2) See one. The power demands for this are vastly lower then those of, say, a prosthetic limb.