Could you do so that soulbound items don't go into the New Transmog group? It's quite annoying having to check each item one by one to figure out which ones I can sell and which I can send to an alt after I have done an old raid.

This will be in the next version.
I'm adding an option for an optional category for unknown but soulbound appearance items that could be saved until patch 11.0 allow you to learn them. Off by default for now.