There are several dates (that we care about, anyway) involved in a wow expansion release:
original vanilla WoW release Nov 23, 2004 (Tuesday)
announced at BlizzCon Oct 28, 2005
BC frnds/fam alpha Aug 23, 2006
BC beta start Oct 13, 2006
patch 2.0 ptr Nov 14, 2006 (Tuesday)
press-release Nov 10, 2006
patch 2.0 live Dec 5, 2006 (Tuesday)
BC release Jan 16, 2007 (Tuesday)
Wrath of the Lich King
announced at BlizzCon Aug 3, 2007
Wrath frnds/fam alpha May 20, 2008
Wrath beta start Jul 17, 2008
patch 3.0 ptr Sep 13, 2008 (Saturday)
press-release Sep 15, 2008
patch 3.0 live Oct 15, 2008 (Wednesday)
Wrath release Nov 13, 2008 (Thursday)
announced at BlizzCon Aug 21, 2009
Cata frnds/fam alpha May 3, 2010
Cata press tour Jun 13, 2010
Cata beta start Jun 30, 2010
patch 4.0 ptr Sep 12, 2010 (Sunday)
press-release Oct 4, 2010
patch 4.0 live Oct 12, 2010 (Tuesday)
Cata release Dec 7, 2010 (Tuesday)
Mists of Pandaria
announced at BlizzCon Oct 21, 2011
MoP frnds/fam alpha skipped?
MoP press tour Mar 13, 2012
MoP beta start Mar 21, 2012
patch 5.0 ptr Jul 20, 2012 (Friday)
press-release Jul 25, 2012
patch 5.0 live Aug 28, 2012 (Tuesday)
MoP release Sep 25, 2012 (Tuesday)
Warlords of Draenor
announced at BlizzCon Nov 8, 2013
WoD frnds/fam alpha xxx xx, 2014
WoD press tour xxx xx, 2014
WoD beta start xxx xx, 2014
patch 6.0 ptr xxx xx, 2014 (xxx)
press-release xxx xx, 2014
patch 6.0 live xxx xx, 2014 (xxx)
WoD release xxx xx, 2014 (xxx)
And before anyone mentions their favorite retailer's posted release date: (we go thru this every. single. solitary. expansion.)
Lots of retailers post a release date that is just their guess at what it might be, and being far enough out that they hope to have a better idea before that date actually arrives.
But they also make it close enough to make people think it really is "coming soon", in order to get more people to order it from them, increasing their own sales.
That's all it is: JUST A GUESS!!!
Everybody, from the general public to fan sites to retailers, will find out the official release date on the SAME day, because Blizz issues a VERY big press release and posts it all over the front page of this site and Blizzard.com. Every WoW fan site and video game site around picks it up and posts it the same day, too.
There is never any secret spilled or anybody knowing before anybody else.
NOBODY knows early, including retailers.
Now on to the guessing game:
My guess is release July 2014, or even sooner.
I would think they have less work to do than previous expansions;
they're not making completely new maps/zones, just remaking the Outland map and zones.
they're not reworking the talent tree.
they're not adding a new race .
they're not adding a new class.