The places of interest have been done for the most part, in another expansion. Having Khara in Vanilla makes no sense, unless the Dark Portal is somehow activated, which then leads to having the Outlands accessible. Newer places means newer gear, which antiquidates the value of T1, T2 and T3. Eventually cool content becomes obsolete as new players simply flock to the best possible.
Which all comes back to WoW 2 .. a fresh start in a new environment, while not crapping up the game with all the undesirable parts of current retail WoW (which is a massive PDF file!).