I haven't figured out a clean solution yet. The solution you proposed will cause a lot of problems when updating materials or geometry because it would be very hard to maintain. Right now all materials and geometry are interactively updated. This flexibility comes with a cost of not supporting two-sided materials.1. maybe duplicate geometry "on the fly" and reclaim memory after loaded into GPU?
Ah yeah, it's section indeed5. not "selection", sectioned model using the "section plane" tool in SU

It works just like in Octane Standalone6. IES light like those I found in 3dsmax plugin
Diffuse Material -> Emission -> Emission Texture -> IES image
I'll check the scenes and will try to figure out what might be wrong.
Thank you!
Fuzzy