That's true, the lack of contents for the midcore players is kind of amazing to be honest. As a raider I would love to be able to touch at those sort of contents, I kind of enjoy playing with midcore players when I'm not raiding they are an interesting part of the playerbase that should deserve more attention, midcore players actually aim for endgame activities but at their own pace, they don't reject the best progression and plan to reach it when it's possible, they kind of touch at everything to say the least.

I would say, something like extreme-mode dungeons while re-using the existing dungeons would be an interesting approach as a solution to this.

(On a personal opinion, I feel a bit downgrade to midcore players to put the "Crystal Tower" exemple in the question to devs, midcore players are actually worthing more than "crystal tower" difficulty level, CT / ST are casual contents :x)