Solved
DITA subject scheme and classification support?
Does anyone know when / if PTC plans to add this to Arbortext? Or what version, if they already have? I couldn't find anything in a search.
I researched this issue a bit more and found that many use profiling to accomplish what subject scheme/classification are doing. It is on the PTC radar, but it is not currently a priority.
It would be helpful to have you convey your needs and ideas to Arbortext project managers at -, and use Your Stuff > Product Ideas > "Create a product idea" to explain your need and pain of not having the desired functionality.