Alternatively, scale up some of the old 50 (Hard) dungeons. There are so many of them that people have never done because you had to go out of your way to unlock a bunch of dungeons that the game didn't even tell you the name of... and this was before the wonderfully helpful Blue Plus Questmarkers. If there has to be a reason to return to them/have them be a higher level, I'm sure it wouldn't be too hard to fit in, but there is just so much un-played/under-exposed content in this game that is just being left to rot. I'm sure a large portion of the playerbase has never played half the 50 (Hard) dungeons, so it wouldn't even feel like recycled content.

Regardless, the ability to diversify such a stale queue is there for minimal effort (mostly number tweaks). I feel having more at-level dungeons to do at 70 would relieve a lot of the max-level boredom and reduce the "lack of content" feeling people get. It wouldn't solve everything, but it would be a comparatively easy place to start.