With two expansions worth of zones called out word-for-word (including all of the WotLK expansions a full year before the expansion came out)... I'd say we should consider this document legit.
Personally, I was hoping for the Emerald Dream (aka Planes set) as the next expansion... but it kind of makes sense to flesh out the remaining parts of Azeroth before delving into alternate dimensions and whatnot (especially with the Emerald Dream supposedly being a reflection of Azeroth without the "taint" of the intelligent races, per WoWWiki).
Although I can't help but wonder... if Cataclysm is indeed announced at BlizzCon... what does that mean for WotLK? After all... we're still waiting for Icecrown Citadel to be unlocked and God only knows what else (ala Sunwell). And if Blizzard holds true to it's previous track-record, if it's announced at BlizzCon, it'll probably be put into beta probably around April-May 2010 and released August-October 2010. That doesn't give Blizzard much time to finish out WotLK (again, given Blizzard's previous track-record with releasing a major content patch every 3 months).