Patch 4.3 (Dragon Soul) went live on Tuesday, November 29th, 2011 ... 6 months ago. Not 7-8.
Here is a compilation of some information and patterns from previous expansion releases, from which we can try to guess a probable release date:
Beta start date to release:
Burning Crusade closed Beta started in early October 2006, and it was released 3 months later, on January 16, 2007.
Wrath of the Lich King started its closed Beta on July 17th, 2008. It was released on November 13, 2008: 4 months later.
Cataclysm Beta testing began at the very end of June, 2010. It was released on December 7th, 2010-- 5 months later.
Mist of Pandaria Beta started March 20th, 2012. 4 or 5 months from the beginning of the Beta would put us at July or August for a release date. A 6 month gap would make it the longest Beta, but that is not impossible-- it has broken the mold somewhat by skipping the F&F Alpha, and we may see a slightly longer Beta as a result (Beta durations have also been increasing, but Mists has
far less questing content to test than Cataclysm). This would put the release date some time in September, possibly October at the very latest (Cataclysm F&F Alpha was 1 1/2 months, Wrath was about 2 months),
if and only if the AP Beta testers took the place of the F&F Alpha testers.
Announcement Date to release:
Burning Crusade's January release date was announced on November 9th, 2 months prior to release.
Wrath of the Lich King's November release date was announced on September 15th, 2 months before release.
Cataclysm's December 7th release date was announced in early October-- also 2 months prior to its release.
This probably means that a July release is off the table, and that, for an August release, we need to see an announcement within the next 2 weeks. If June goes by with no release date announced, we're probably looking at a September launch.
PTR x.0.1 testing:
There has been indication that 5.0.1 is being prepped for the PTR.
Cataclysm's 4.0.1 patch and Wrath of the Lich King's 3.0.1 patch both went live on the PTR 2-2.5 months before the expansions themselves went live. It's possible that we will see the 5.0.1 PTR before we get an official release date-- if we do, we can probably extrapolate that a release date announcement will follow within a week or two, and that launch will be 2 months after.
If 5.0.1 is nearly PTR ready, then Mists is probably 2-3 months from launch.
Brewfest:
Brewfest adds an interesting complication to predictions. There are updated Brewfest items in the Beta files, implying that Mists will release in time for Brewfest-- or, at the very least, that Blizzard is acknowledging that a pre-Brewfest release date is/was a distinct possibility/intention as of May 15th, 2012.
Brewfest this year begins on September 20th-- assuming Mists will come out in time for Brewfest means that we can scrap all predicted dates that occur after September 20th.
In conclusion:
Since we have neither a release date nor a 5.0.1 PTR, Mists is most likely at least 2 months away from launch, probably more like 2 1/2-3 months. This puts us at a probable late August-through-mid September release window as the most likely release window, with early October as a possible (but less likely) release date.
Potential release dates are an optimistic August 21st or 28th, a realistic September 4th, 11th, or 18th, and a pessimistic September 25th, October 2nd or October 9th.
Taking Brewfest into account, August 21st through September 18th are the release dates that would be in time for the holiday.
Personally, my money is on a release date of either 8/28, 9/4, or 9/11.
Here's an article from WoWInsider that contains/confirms some of the information I've posted here, and supports/matches my own prediction.
As it says in the article, we can guess and predict all we want, but we can't ever know with 100% certainty until the date is officially announced.
This means that Mists should most likely release in late August or early September, 9-10 months after the release of Dragon Soul-- not 12 months later like Cata was to ICC. Even an early October release (the "late" window of my prediction) would be about 2 months shorter than the gap between ICC and Cata.
Implementing additional content would likely delay the release of Mists, rather than allowing the development team to focus on the expansion, and would then put us into that 12-month gap that they said they don't want a repeat of.
This is all not to mention that we should see the 5.0 pre-expansion patch at least 2 weeks before the expansion itself goes live, bringing with it a mass of class and talent changes, along with the Theramore scenario. There's some content right there.