Hey Paul, thanks for your question.
I understand your reasoning as it was the same thought process I had when considering using a DFS namespace to mask the underlying server hosting the file share for the config-store and directories of ArcGIS Server. In theory, it makes sense and should not play into the 'immediate consistency' requirement of the documentation (https://enterprise.arcgis.com/en/server/latest/install/windows/choosing-a-nas-device.htm). However, in practice, we have found multiple failures occur, especially in the publishing process. This has been reproduced in multiple test environments with the most simple DFS targets (hosted on the same machine as ArcGIS Server) and typically results in <10% failure rate during publishing. That means that for a low number of services published, the effects may not be observed, but under a production load with a large number of services being published the effect becomes much more noticeable.
So for practicality's sake, we have determined that DFS (even single-target) is not supported due to the observed behavior when attempting to implement that technology.
Hope that helps!
-- Chris Pawlyszyn