FYI, transmogrifying armor isn't as easy as A = B. The code won't allow the existing method of swapping weapon visuals or character visuals to be applied to armor. I do not know if there is a technical limitation causing this, or Larian just didn't want to add the code for it, but armor transmogs currently either require manually editing each file, or scripting that makes my brain bleed. I saw how the Transmog Lite author does it and reading all of that scripting hurt my brain. They essentially code for individual armor pieces.
I do agree, though, that it would have been a good base-game function. They could have tied questing to it, or a made it a gold sink.