Speaking of that elephant....
I was talking about this with a friend and with things honestly looking pretty bad with Majors right now after the events of today especially, do you recast, or seeing as Majors only appeared as Kang/He Who Remains in one episode of a show and in one movie (and honestly he looked kinda wimpy both times), what if, using the multiverse, they brought Josh Brolin back, this time as King Thanos, the Thanos who won?
The issue with recasting Kang imo is every version of him would look like Majors canonically, although I guess they've recast before. Doing something like King Thanos though would bring back a fan favorite villain that's even more powerful, it wouldn't ruin any new villain by having them shoehorned in, and it would represent a real threat for something like Secret Wars and the only way to defeat him is to call on all the different versions of characters from different universes to come together to stop him.
Obviously the likelihood of something like that happening is very low and they will just recast though, although i'm not exactly sure who they would find that's as eccentric of an actor and fits the role so well. Donald Glover comes to mind as far as fitting the eccentric nature, but he doesn't have the physicality of Majors.