Problem is, if it were possible to generate meaningful amounts of energy (relative to what we are talking about, skiing) from piezoelectric devices this technology would be being used other places where it is more profitable and beneficial. If Head came up with some novel technology here it would actually be in very high demand from other industries. At best, this is technology that is cobbled together from existing pieces. Suspending disbelief is one thing, but you can't relate this to actual revolutionary discoveries. Head hasn't changed physics, real groundbreaking technology is not created by sporting goods manufacturers usually. Pretty much every advanced material or innovation in skis is a trickledown from military, aerospace, medical, or some other industry.
It doesn't have to generate meaningful amounts of energy. Just change the electrical environment of the material. Anyone who has ever done a titration experiment in high school chemistry knows it's that one drop that will cause the colour change. A slight difference in the electric field can cause a big change in material property. I can see it causing soft skis to become stiff skis. It's not the piezo electrics that is supplying the energy; it's just you noticing the effect of having stiffer tails.
BUT I still don''t have my answer as to what the heck's the difference between KERS and the other earlier chip intelligence technology, other than one answer that now it is making the tails longitudinally stiffer and it wasn't before; it seems rather strange that it wasn't before.