Quote - Even if some product shaders are too complicated to have GC injected by a 'generic' GC injector script ...

I suspect that an algorithm could be devised to deal with any shader because they aren't true networks (they're acyclic) so it must be possible to work out where the sources are (the sinks are the inputs on the PoserSurface node) and so you'd be able to assign a GC/non-GC state to every edge, and that would tell you where you'd need to insert GC or anti-GC.