If I'm not mistaken, Les Schwab pioneered the use of walnut shells in snow tires. The company sold recaps that had them embedded in the rubber. Plus, the rubber compound was fairly soft so it would hold the slippery road better than a hard rubber compound.
From what I hear, they don't do a lot of recapping on passenger car tires anymore because they sell new tires almost as cheap as recaps.
Schwab does a lot of sipping on regular passenger car/pick-up tires at his stores now. What that entails is making a whole lotta cuts about half an inch apart, about a half inch deep, clear across the tread face. I have mine done when I buy new tires and it costs about $10 bucks a tire.