He's referring to RIM lighting technique that Double Fine's new game Broken Age uses. There was an email update the other day
Sources:
http://www.doublefine.com/dfa/content/update_11_character_lighting/ (Backers Only)
http://www.kickstarter.com/projects/doublefine/double-fine-adventure/posts/474494?ref=email&show_token=1befdfafcf25f4a2 (Scroll down to Lighting)
http://www.brokenagegame.com/ (Trailer)
Where {Red,Green,Blue} is a light direction multiplier and the scene lights are added to the final pixel color.
I had a similar conversation with one of my friends and I think we concluded that it's a pixel shader technique similar to normal mapping. Really, as long as your drawing the Spine animation (with normalized uv coords), you could simply turn on your custom pixel (fragment) shader, bind your RIM as the second texture, do a lookup, a DOT product, a multiplication and an addition.
The catch is that you need to pass the rotation into the fragment shader, possibly in the second UV spot. That rotation is used to DOT the rim texture light to redistribute the lighting value across the right channels based on the slot rotation. Negative values would clamp to zero and I'd suspect that MAX two lights could be blended.
Each light color would be passed in as constants to the fragment shader.
In any event, it's not really a Spine problem. It's a nice feature, but not really core to a complete product. That and everything I described could be done currently without modifying Spine at all.
My two cents.