just use Kaluuya. ride the hot hand. open with everyone confronting him for turning on T'Challa, put him in a brief crisis mode, and have him atone for his sins for the first act, let Namor attack or whatever and then have them reluctantly give him the herb and let him become Black Panther.
marvel already over-corrected the lack of female heroes, now they're about to be predominantly female. we're good for a while, no Shuri. she's built like a twig and has a good role already. i'm sure i'm a broken record at this point
maybe the Okoye series (unnecessary imo) will drop prior to this and they can beef up W'kabi's path to BP in that so we don't even have to waste scenes in the actual movie