With 6.2 the recent announcements concerning the Crystalized Fel, it's looking like we'll be doing Archimonde until November.
Bringing us to Blizzcon.
In which case we can most likely expect the next expansion to be announced.
Beta is on average *five months in duration.
November + 6 Months, has us at May 2016 for a release time frame.
Just shy of a year of HFC if they don't add anything in the interim. But that doesn't seem likely considering we're still upgrading our rings off of Archimonde.