I'd suggest having a pack that clips onto the back of the shoe (mostly so it doesn't get broken off if your shoe brushes against the side of something, also it's not as noticeable) but low profile enough that it doesn't irritate the back of your foot. A belt mounted battery would be nice but yeah the wiring could be difficult. Maybe have it snake down and rest along your upper leg and generate energy from that, instead of all the way down to your shoe?
Hmm, those are some very valid points. I like the idea of it clipping onto the back of your shoe. Thank you!