It's certainly possible. A 19th-century occultist named Helena Blavatsky famously claimed she learned from "Masters of Ancient Wisdom" in Tibet.
Any or all of these could have inspired Lee & Ditko.
It's certainly possible, but given current societal trends, I think it more likely they'll go for someone young, possibly Wiccan or a new character. I also think said Supreme will last just long enough for Strange to come back in time for the movie, but I'm a huge cynic these days.