SE seem to not have wanted to add extreme versions of dungeons. They thought about it but never really committed to it. I wouldn't mind instead of that getting special achievements with rewards to make the content more challenging. Things like:

- complete in under x minutes
- complete without a tank or healer or both
- complete without using x/y/z skills (like the tank not being able to use provoke or aoe skills)

Etc. etc. Or any combination of the above. These could be challenging enough while remaining optional enough to keep some entertained.