Well here's one thing I attempted to already make clear: The new world is assuredly amazing. I don't doubt that. Bring on the Shattering, for sure, can't wait.
The point is that people who hear of the old world, and assuredly those who are JUST NOW entering the game (who more specifically are seeing a world vanish before their eyes, a world they will never experience) will want to see it. Just because the new world is better doesn't (and more importantly, won't) justify removing it. A CoT instance wouldn't be so hard, really.
It's strangely blasphemous that the thought of not preserving Old World Azeroth has come to such widely accepted fruition.
Truth of the matter is this. I would love to go to the original Woodstock concert, but I can't because it happened way back in 69, and I wasnt born till 75. Same thing here for the new players, the world is forever changed. Deathwing broke it, and now they get to help try to fix it. It may seem unfair, but I think that it is a bold move on Blizz's part. No other MMO has EVER gone back and completely redone the original game world for their universe.