There is a serious difference between mangaka creating their own version of D&D, and a D&D setting inspired into Japanese folklore.
Playing is not only throwing dices over a tabletop. When somebody is creating characters and stories using D&D mythology, they are also playing D&D in other way.
Maybe the key is not to hire famous mangaka, but allowing D&D as a showcase for new and unknown talents. And prestigious artists would rather to keep controll about their own creations.
Other point is TTRPGs worlds are designed to happen interesting event in different places, while ordinary literature is too focused into the story with the main characters. I mean after the end of these plots then those worlds become "boring places" because the big bad guys have been defeated.
Some times people would rather to cook the same recipe but with a different style. For example a Japanese writter would create a male main character, and maybe his "harem", a group of cute female sidekicks, but a Western writter would rather a mixed group, not only male and female, and not necessarily romantically linked, but people from different origins, and maybe some "half-blood".
A Japanamerican artist could dare to say any things a native Japanese wouldn't dare, for example a denunciation of anachronistic discrimination against the burakumin (a discredited caste), or tyrannical elitism where if you aren't number one then as if you as if you were worth nothing. Or the artist could launch questions about the sense of honor. For example saint Thomas Moore was executed as traitor and saint Joan d'Arc burnt as a heretic and excommunicated. Did they did with honor or dishonor? Or the artist could use the plot to report the xenophobia, because "being locked inside a bubble is also a source of corruption like stagnant water in a swamp". Different nations could follow different codes about taboo threats.
I have suggested several times in the past WotC could be the sponsor of Japanese game-live shows. This could be the opportunity of young but unknown aspirants to seiyu(anime voice actor).
And Korean artists also could be invited to create their own version of D&D. They shouldn't reject it because this could be a open door to enter in the Western market and promote their own "soft power".
