It has been a while since I've read through my entire collection, and each writer does their own thing, so what the truth is can only be opinion, but this is how I am looking at this whole thing:
The aged Genghis in Triumph and Torment made a bargain with the Vishanti at the dawn of mankind. Depending on how you look at it, it makes him at the very least 7,000 years old and possibly very much older. I do believe Strange once mentioned he was part of the Aged Genghis' sect, which to me means he follows the same path of magic Strange does, and it is well know that Strange's primary gods are the Vishanti, so it fits nicely.
I think it is likely that during that time, sorcerers that were capable of traveling throughout the multiverse, probably found their way around the world. It was likely they would occasionally teach a few of the people with mystic potential a few things. Not just Asian people, because I think talent for magic is much less common than some writers feel (those who think all you need to do is read a book and voila, teleporting about the world) and they will teach those the path of light, before they find the path of darkness. Perhaps they even visited Europe on occasion.
I see that with this whole idea of the Ancient One being a legacy title, why not have it passed down through thousands of years. Perhaps they will combine the Aged Genghis and the traditional Ancient One, with their Asian background, into one character. Perhaps even he was the one who taught the now current Ancient One, or a previous one of the distant past. Perhaps it is also the role of the Sorcerer Supreme to eventually become the Ancient One for Sorcerer (or "ess") Supreme as they evolve along their mystical path, who can be from either gender, any color.
Personally, I think they will show the Ancient One as a spiritual form, neither female or male, that acts as a conduit to the gods of other dimensions for the SS, Tilda is great at androgeny. Either way I don't object to Tilda playing the character. What I care about is that Wong is played by an Asian Man, and is giving a strong personality, and his own story as an inherited protector of the SS. Everyone needs back up.
Strange welcomes the melding of eastern and western worlds, and all they have to offer, but I would not say he practices Eastern magic, he practices inter-dimensional and universal-based magic. He takes everything that this world has to offer to enable him to protect the world in a better manner, and skipping out on half of it would be neglectful.