Of the mostly female directors in Marvel's rumored shortlist from October 2018, the most intriguing name mentioned was Dees Rees. Rees has been a clear rising talent in the film industry, going from the small indie Pariah to the HBO biopic Bessie to the Oscar-nominated Netflix epic Mudbound. If none of these outstanding credits scream "director of a Marvel movie," remember Rees also directed an episode of Philip K. Dick's Electric Dreams and, when given the chance to do whatever she wanted for a Walmart commercial, made a lavish space opera. She's pretty much waiting for the chance to do that for a full feature.
In addition to her obvious talent, hiring Dees Rees would certainly save a lot of face for Disney. The big concern with Gunn's firing was that Disney was capitulating to the alt-right. There's zero chance that hiring a black lesbian director could be seen as "capitulating to the alt-right." The potential downside for Rees, however, is that, given this job's scrutiny, it's possible she could receive worse harassment than Gunn ever did.
It's kind of weird that Michelle MacLaren hasn't got a movie made yet, is it not? She directed many of the best episodes of Breaking Bad and has touched practically every large-scale prestige TV series since, from Game of Thrones to The Walking Dead to Westworld. She almost directed Wonder Woman, but got replaced, and the two films she's currently signed on to, The Nightingale and Cowboy Ninja Viking, are dealing with production delays.
Cowboy Ninja Viking just so happens to star Chris Pratt, so she has an in with the cast of the Guardians movies, who will need to approve any new director choice after their outspoken opposition to Gunn's firing. MacLaren's one of the other promising names on Disney's shortlist, and feels like one of the more likely choices. It would also be a fair trade between WB/DC and Marvel, each picking up a director fired by the other studio.
THE WACHOWSKIS (AT LEAST ONE OF THEM)
News of the Wachowski sisters' retirement has been greatly exaggerated. Just this January, Lilly Wachowski became attached to co-write and co-direct a new TV series titled Work in Progress. Perhaps Lilly and Lana Wachowski aren't working together anymore, but at least Lilly is working, and one imagines Lana could be convinced to as well if given the right opportunity.
Either or both of the sisters would be awesome to have on board for Guardians 3. While it might seem unlikely that such idiosyncratic filmmakers would work within the Marvel machine, Gunn's Guardians films already stood as idiosyncratic among the rest of the MCU, and the Wachowskis could do wonders with the material. They know how to stage action amazingly, and the series' themes of found families are right up the Sense8 creators' alley. While the Wachowskis' work hasn't exactly been consistent, having them just direct Guardians 3 while keeping Gunn's script might do wonders to provide some focus.
Bradley Cooper isn't the only actor-turned-director among the Guardians cast. Karen Gillan, who plays Nebula in the MCU, has directed three shorts and one decently-reviewed indie feature, The Party's Just Beginning. Given the number of directors handed the reigns to major blockbusters after just one feature, it wouldn't be unprecedented for Gillan to take control of the ship for Guardians 3.
We don't even know if Nebula's going to be alive in the MCU post-Endgame, but if Gillan's no longer a star on-screen in the MCU, she might be excited about being active behind the scenes. We also imagine that, given how much the whole Guardians cast loves James Gunn, Gillan might also be able to consult with Gunn and keep her version of the film relatively close to his original vision.