It baffles me that we still have so many arbitrary restrictions on transmog. If anything, like many people have already said, we need less restrictions and more freedom! A cloth wearing DK or Warrior? A Moose Firemage? Transmog your Polearm into two fist weapons? Just look at artifact weapons xmog where a lot of normal "rules" suddenly dont apply anymore.
And dont come with your "engine limitations" or "animations" bullshit, there's loads of crazy stuff you can pull of by combining different toys. Just let people enjoy the game the way they like it. It would also free you from having to enable dual weild on some specs just for the sake of xmog. Let us collect transmogs regardless of character class and armor / weapon spec. Just cut down the barriers and people will start to get creative and look way more different.
Let transmog be what everyone wants it to be, a fun way to enjoy the game with your character.