Well, in OpenGL, we have ambient, diffuse, and emissive shading, and maybe some others, where most take an rgba value (emissive ignores the alpha component -- so to do transparency you have to set the ambient alpha value). I guess you could define a shader that says which ones to use and the values, and then the vertex group would have a shader list atom that had n shader atoms (1 per vertex). We should probably think it through before diving into it. What you have is probably fine as a first cut. The format is extensible, as you say.
Transparency is part of ambient alpha shading, though, so it will be an issue as soon as we have zone bounding polys (that keep you from walking off the world). Also, being able to tag polys as solid or not is a must, but maybe that should go into another atom?
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