This one was about “special” properties in Python, in general. You can’t currently make custom Python props in certain types, like ramps, curves, or ID linkers. This is why there’s no colorramp node in LuxBlend, and why the image node needs to be pointed to files on disk rather than the much more elegant link to an image datablock. (in the “classic” mat editor we get around that one by hijacking the regular “Image” texture type).
Custom curves, ramp and ID-link props in Python would be nice.