Bryan Fuller is the co-creator of Star Trek: Discovery and originally in charge of the casting. As I've previously written, he wanted Laurence Fishburne to play a Klingon on ther series and had some other differences in mind, too, like Paul Stamets [Anthony Rapp] being an Andorian.
Another actor he was reportedly in talks with to play a Starfleet captain was Gillian Anderson, better known as Dana Scully from The X-Files. [via Screenrant] An Emmy-Award winner, Anderson also portrayed Dr. Bedelia Du Maurier, Hannibal's psychotherapist on Hannibal, a series that was developed by Fuller. It seems he had an idea to bring most of the cast of Hannibal aboard Discovery.
Honestly, though, having Anderson as a captain isn't a bad idea at all. She plays the perfect authoritative figure [see her role on The Crown as Margaret Thatcher] and, after having spent time on The X-Files which ran for eleven seasons, would fit right in among another science fiction series. Though she didn't end up playing a role on Discovery, there could be another opportunity for her to fit into the franchise.
Anderson has never left science fiction and works well within the genre. Her next film will be Tron: Ares along with Jared Leteo and Jodie Turner-Smith. And it's easy to picture her as a captain (or even an admiral) in Star Trek: Strange New Worlds or the upcoming Starfleet Academy. Anderson gives off Captain Kathryn Janeway [Kate Mulgrew] vibes, which would serve her well in the world of Star Trek.
Now that Fuller has pitched the idea, another showrunner should jump on board with casting Anderson for Star Trek. She could easily even be the star of her own show in the franchise. Her character, Scully, dealt with all sorts of creatures and unexplained phenomenon in The X-Files. Trek's aliens would be a walk in the park for her!