From the outset should define what we mean by "new content"?
On the other hand, there is many old existing content which is not necessary for anybody. I doubt that there are a lot of players that are explored in detail all the locations and to fulfil all the quests (not only those which are necessary for achievements). Also, there are old world dungeons, where many players had never been and doesn't want cause loot is crap. Let's see if for example to Shadow of Vanaheim expansion. Many players needed it? I mean cases when content as if exists, but the interest is low. From my point of view such cases in game are too much. We need to answer the question of why part of the old content is unnecessary in order to avoid a new unneeded content.