A lot of elements in Retail are utterly incompatible with Classic.
Best example: M+
Literally any dungeon must fit into this time trial mode, else it needs to be separated from this system entirely.
Which leaves out the fact that Blizzards track record on content "inspired by Classic" isn't too great, Ashran was promoted as this sort of "modern AV" and failed pretty hard.
When i queue up for Epic bg's, i rather get AV over anything else, especially Ashran.