Siege of Orgrimmar (Patch 5.4) was released in Oktober 2013, Hellfire Citadell (6.2) was released in July 2015 and after 14 months of no new content and the release of Legion in September, the next content patch could follow in 2017. (No, 6.1 was no Content patch, even Blizzard had to admit that)
So not only do we get less content, we even get it less often for the last 3 years now and the trend will pretty much continue like that. So 7.2, if there even is one, will be released end of 2018 or early 2019.