IMO, they should take mythology from other continents like Asia and Africa and South America. There is SO MUCH MORE out there than old European myths. Not that I don't enjoy King Arthur and Tolkien.
I don't think some (most?) other cultures really have any interest in exploring their past and mythology in a fictional way like DnD. Plus they don't have a Tolkien like author that can totally reframe their mythology into a format that lends to spin off variations and "Adventure" stories that encapsulate the cultural values so well. If you really step back and look at what Tolkien did, it is a LANDMARK event in western literature. He grabbed from many aspects of European mythology, synthesized it with a heavy dose of Christianity, and hammered it all into a narrative that emphasized all sorts of western civilization values like rugged individualism, loyalty, "good vs evil", personal destiny, etc.
But other cultures don't always share those values or have the christian basis, so it's difficult to really create a fantasy story for them (as opposed to just transplanting Quetzalcoatl for Odin, Xolotl for Loki, etc) and doing a palette swap thats still really a european story with a Aztec coat of paint. Someone steeped in that culture has to collate it, keep the critical resonant parts, and then spin a story and create a world that reflects THOSE values and sets up a framework for other authors to riff off it, but in a way that feels authentically Aztec/Mexican instead of just Christian/European.
The Chinese have this with Middle Kingdom stuff, same with the Japanese. Translated versions of their stories can be quite different in feel than a typical western fantasy and not just because they wear different armor, wield a katana instead of a longsword, and fight monsters from a different book. The goals of the characters, the very NOTION of a group of disparate characters getting together for a road trip to stop a great evil....all that stuff is western mythology/Christian values using Beowulf, Canterbury Tales, Norse myth, Greek heroic journeys, etc that don't always have parallels in other cultures. There is often a sense of fantastic unreality, no need to make a logical flow of events, less concern for internal consistency, you see this in the anime and manga, how some cultures place less value on narrative drive and more on "in the moment" events or other qualities. Norse mythology was like this as well, they are all over the place in what charactgers could do, WTF Loki even was or what he stood for, etc but Tolkien put this much more rigid pantheon over it all that we have adhered to ever since.
So, TL
R, any drive to create "non european based fantasy stores" really need to be from non-europeans inventing their OWN version of "fantasy", not just change the drapes in the same old house and call it "new".