There's a certain Orientalism that underpins a lot of 20th century pulp stuff, and that seeps into the comic books of the 60s through 80s in a big way. One example is the backstory of Doctor Strange - formerly a gifted neurosurgeon who loses his fine motor control in a car crash, Stephen Strange travels the world trying to be healed before discovering a Tibetan mystic who initiates him into the magical arts. That mystic is the Ancient One, pretty much your standard wizened old Asian wizard figure, and he's a pivotal part of Strange's story.
Not that there's anything wrong with Asian mysticism (Strange's manservant Wong is probably a bigger problem in a modern adaptation) but the Ancient One treads on mystical minority stereotypes, and could be handled very poorly in a modern setting. So what's the answer? Maybe avoid the stereotype altogether and cast way outside the box - like a delightfully weird, seemingly already mystical white woman.
Tilda Swinton has been offered the role of the Ancient One, and by having her David Bowie-esque, androgynous and timeless self in that part the character takes on very different and new dimensions. Of course there's the question of whether casting a white person in one of the few Asian roles in a comic book is 'erasure' of Asians.
This feels like a lose/lose to me, politically - there's no version of this movie where the wise old Asian, no matter who plays him, goes unscathed by criticism - but a win/win to me cinematically. Swinton is fucking awesome and she's usually playing magicians anyway, even if they're not specifically specified as such in her films. If they cast Swinton this could mean the Ancient One has a large role in the film; the character hung around for quite a while in Dr. Strange's original solo stories, eventually getting killed (by Strange! To stop the evil Shuma Gorath from using his body and mind!) and allowing Strange to ascend to the role of Sorceror Supreme. The Ancient One himself transcended to a higher level of existence, and he has shown up a couple of times since.
If you ask me a story wherein The Ancient One transfers the title of Sorceror Supreme to Strange is the right mix of in media res and origin story - Strange's origin wasn't even told until he had appeared quite a few times. Meeting Strange as a sorceror who is working with the Ancient One, and then shouldering the burden of becoming Supreme to save this dimension from Mordo or Shuma Gorath or Nightmare is exactly the correct story to tell in the first film.
It'll be interesting to see the response if Swinton takes the role. This sort of genderswapping is cool, for sure. Removing an Asian character is less cool. What I'm curious about is how many people who will have an opinion will have any knowledge of Dr. Strange at all, considering the fact that the character has rarely been able to even sustain his own title over the last sixty years.