So, I want to step back. Is this functionality really something that part authors will use, and is it useful enough to justify implementation?
I'm pretty sure you could get the same rendered results by creating the LDraw geometry and then saving a PNG from a top-down view in LDView with transparent background enabled, then using that PNG as a texture. I will readily admit that doing it that way is a kludge, but if all people want is the ability to model their textures in LDraw, it does the job without requiring any spec or renderer changes.
Having said all that, if part authors believe that this will be genuinely useful, I'm not opposed to implementing it.
I'm pretty sure you could get the same rendered results by creating the LDraw geometry and then saving a PNG from a top-down view in LDView with transparent background enabled, then using that PNG as a texture. I will readily admit that doing it that way is a kludge, but if all people want is the ability to model their textures in LDraw, it does the job without requiring any spec or renderer changes.
Having said all that, if part authors believe that this will be genuinely useful, I'm not opposed to implementing it.