I saw a post today that ruffled my feathers (not linking to it for obvious reasons). It basically inferred that there is concern that Blizzard only intends to revamp old content from here until eternity, just like Disney and their movie vault.
I've written a post about this before. The main theme of Cataclysm is changing the world, including the old world. It desperately needed to be done. They've taken that theme and run with it and I for one think this has turned out beautifully. I don't think this means our next expansion will be "Return to Outlands" or "Wrath of the Wrath of the Lich King," although I wouldn't be opposed to revisiting these zones, but with new new dungeons and content.
While some people may be disappointed with the revamping of old dungeons and upset that it isn't "new" content. They did make changes in these dungeons. They aren't exactly the same as they were before. They aren't just scaled for 85. Deadmines and SFK have been revised to progress the storyline of their given zones, not to mention that they include new boss fights with new mechanics. Many many veterans are enjoying the heck out of Deadmines and SFK as Heroics.
I for one am glad they are bringing ZG and ZA back. I am not a Wrath or Cataclysm baby. I have played these dungeons while they were real content and I was saddened to learn of their removal from the game. My understanding is that these new 5 man dungeons (like the others) are not going to be exactly as they were before. They are going to progress the troll storyline. They may have new bosses and new mechanics combined with our old favorites.
I might have cause for concern if I got wind that they were turning Karazhan into a 5 man Heroic. Then again, I might welcome that change as well. My feeling is that these changes are a good thing. I think it is always a good choice to make old content relevant again. Would you have rather they left ZG and ZA as they were, a dungeon people only went to in order to farm for mounts?
I think Pewter has put it best here. In terms of pure content released per patch, we're way ahead of WotLK.