Very cool idea... but I'm incredibly skeptical of the obsolescence cycle.
First, what happens when the string gets wet? Well given that most fabrics expand and lose friction... the bike fails.
Second, as oils, dirt, and solvents work into the string is also going to fail.
huh. This isn't going to catch on for bicycling, but the general idea looks like it has awesome potential for harnessing waves on water, as it is converting irregular reciprocations into torque power. Got ocean swells?