The Hardy Boyz (Matt and Lita's relationship, along with Jeff's struggles with substance abuse).
I know redemptions are not a theme of show, but it would be somewhat refreshing (and some of the above picks are applicable). I don't really need a tragic ending to be invested in these kinds of stories.
WWF Steroids scandal & ring boy scandal
Magnum TA`s injury
Juana Barraza/La Mataviejitas – lucha libre serial killer
The death of Misawa
Dick Murdoch & the KKK
The Insane Clown Posse
Wahoo McDaniel shooting Dick Slater on the leg while pistol-whipping some wannabe tough guy is humorously dark. An episode about Native American mistreatment in North American wrestling would be a great subject to cover. Give the First Americans a chance.