Darn, I wish you'd seen it too :). Sounds like you came to similar conclusion I did -- using C++ templates to stamp out v8::FunctionTemplate and ObjectTemplate instances.
I was pretty happy about how Gin turned out and always thought it would be nice to put it on Github where it would be easier for people to reuse.
But at the time Chromium still didn't allow all the modern C++ features, so Gin had to depend on base::Callback, which made it hard to extract cleanly.