For example... say I wanted to modulate a material zone between two shaders, using a black and white control map, plugged into a blender node...

...being able to load, say, a skin shader, and then append the nodes from a BBGlossy2 metallic shader ,and modulate between those two, to create some sort of cyborg effect.

Or, with what I'm doing currently, applying BBGlossy2 to the textures in Jack Tomlinson's Baroque Grandeur, I could more easily set up that modulation between the metallic gold paint look I'm trying to get with BBGlossy2, and a shader to emulate plasterwork (having created my black and white blender node control map by modifying one of the supplied specular / bump data maps).

The option to load-append from an mc5, into a selected material zone, would certainly be a big time saver in doing that sort of stuff...