Then lets add the Cataclysm Azeroth aswell, it wont harm the game at all - people level in Dungeons anyway so most wouldnt even notice. It would just be more fun to level 1-60 again!
Transmog aswell, it would just make people farm more things and add activity!
Oh, and since it goes with the theme - lets add Demon Hunters! We all know tanks are hard to come by, why not introduce a new class that would encurage more people to tank?
And why not add a Battle Royal version of Isle of Conquest?
None of these things harm the game, they just add value and are SO comparable with auto-loot (which has always been a shift+loot option - since Vanilla, even before it was in the interface)
Its not about how much it harms or doesnt harm the game. Its not about how much downsides it has or how many other players would or wouldnt be affected by it in their everyday gaming. Its about how close to the objective original version of TBC it can be.