Boy, I hate to rain on the parade, but of course this thread is really about how it's
not a car paint shader. It's multiple layers of geometry each with different shaders.
As usual, we find clever (and effective!) workarounds, but at the expense of optimization and efficiency. A layered shader that doesn't require us to duplicate the surfaces is what's really in order! But it's nice to see, isn't it? In fact, a layered shader should produce results very much the same way as this workaround, only more efficiently.
Good job... I bet we're all excited for the day when the workaround isn't needed anymore.
_Mike