It appears that you can't use TextureSets on armor, or the game is bugged and Bethesda never fixed it. I had an issue with environmental effects not working until I switched to a NIF that didn't have a TextureSet attached. I've spent days trying to figure out what caused that.
According to Statcounter, the desktop operating system market share for Linux in the US is up to 9.59% so far in July. I'm not sure I buy this yet. Could it be the Steam Machine effect, or bad data from Statcounter?
Right now, I'm learning how to import textures into the mod, and after reading this thread, I've just realized how ancient the Creation Engine is.
https://forums.unrealengine.com/t/what-image-format-do-i-need-and-how-do-i-implement-it/287448