Brilliant!
I'd want to see more about how you'd keep the vibration in modes that would still make the end generators work. Does the vibration have to be in the fundamental mode to work, or would the generators still work if it move up into one of the harmonics?
Demonstrated on a slinky, below:
It seems to me that something could be done to adjust the generator ends to account for a variation in angles. I'm thinking an array of small generators might work better than trying to stretch a single strap across a large gap.