Most of the ones I can think of are ones it would be hard to find people to interview for.
The death of Misawa or the NOAH/All Japan exodus - there's a lot to dig into with how he basically worked himself to the grave because he felt he couldn't stop.
The Mass Transit Incident - Paul Heyman won't appear and New Jack and Eric Kulas are both dead but archival footage of testimony could be used since there was a trial and New Jack wasn't shy about talking about it. Maybe get the paramedic who attended to Kulas for a first person perspective we haven't really heard.
Tammy Sytch - Particularly if the death of Chris Candido can also be talked about as that seemed to contribute to her never ending spiral.
Mike Awesome
Hana Kimura
The Saudi plane incident - You'd never get WWE talent, but a few of the people who have since left might be willing to go on record with their own experiences of being on the flight.
The rise and fall of Chikara Pro - A fair number of ex-Chikara talent might be willing to go on record here if not Quackenbush (and even he might see it as an opportunity to mea culpa for his part in it and repair some of the damage). Of all the Speaking Out possibilities, this one feels like it has the best chance of happening because it impacted a whole company and there aren't a shortage of people to interview. I could see the former Chikara names who weren't involved in the shady stuff seeing it as an opportunity to reclaim aspects of their own careers that are basically ignored.
Lucha Underground and their contract fuckery - a lighter one...at least the deaths in this episode would all be kayfabe
Dick Murdoch - actual Klansman
Muhammad Hassan - guys career was basically killed over a stupid angle and the worst possible timing
The Graham Family - this one would be really depressing, but talking about the cycle of grief that suicide can create would be important
The retirement of Magnum TA - one of the great "what ifs" in pro wrestling history.
Brooks v. Colton - get Punk and Colt to sit down and talk about the toll the Ammann lawsuit took on their friendship. Neither have really publicly talked about their falling out and it would be a potentially cathartic episode if they could mend at least some of their broken relationship and talk through their own sides of the story on the record.
The Death of Brodie Lee - It would be rough, but it's an episode that wouldn't be about doom and gloom since he was so beloved.