Developers announced that there would be no 5.5 patch, which means that until we get to the transition patch (giving us our new skills and tweaked talents) we will be in Siege of Orgrimmar.
How long will we be in SoO?
From Cata, DS was pushed on November 29, 2011 and then 5.0 came out on August 28, 2012 (approximately nine months).
From Wrath, ICC was dropped on December 8th, 2009 and Ruby Sanctum on June 22nd, then 4.0 was released on October 12, 2010 (approximately 8 months).
The interesting thing is that the announcements for each of these expansions came out almost a year before their announced expansion's release. So, does that mean we'll be raiding in SoO for over 12 months?