I think he is refering to HD textures, as far as I know you can update texture images (placing them in same folder system as the game once) and having the game load them (most of them).
If it was against Blizz intentions they would disable this by making the game only load files inside the MPQ and not in other folders.
But no, I have no info on such a "HD graphic pack" sort of thing for WoW.