Honestly I find it hard to believe that they don’t know because you see the volume of change when new class/races are released.
Look at how many people rolled and/or changed to Gnome when they opened up Priests/Hunters.
I think the problem stems from a combination of scope/capacity (cost) for certain classes, especially druids, and this internal battle around lore and what is/isn’t flexible enough to adjust.
They clearly already have a pipeline for armor because you can be on any race and “view” any item in the game on that race and it appears fine. So the only real complexity is forms (Druids), Mounts (Pally), Totems (Shaman), Demon Form (DH, although I’d argue they could just leave it the same as is it now for all races), and whatever they would do for evokers.
That’s not to say this wouldn’t be costly to do but if you look at just how much content gets pushed out even within a single major patch. Trading post is a perfect example, take a few months of that content to instead do this. I love the trading post, but I’d love this more 