Again. As it was already discussed times and times again. Besides animations, new modes are not compatible with old non-adjusted armor, old models aren’t compatible with the new and old adjusted armor. Same with mounts by the way.
If at some point blizzard decided to make 2 completely separate graphical representations for old\new models that involve 2 different variations of animations\armor and weapons placement\interactions\mounts placement\etc. then more power to them. But I’d not hold my hopes high.