I'm not sure if Kojima is the kind of developer that would struggle to find a publisher that isn't a platform holder, but I do hope Microsoft is indeed going all in with plans to invest more heavily in japanese games. It would be nice to see more higher budget games that aren't from the usual publishers. Some of the people who recently started their own studios could really use Microsoft's funding for their next titles, like Toyama or Nakamura. They could also be a good potential partner for genDESIGN, assuming their deal with Epic will be a one time thing, and they'll go right back to shopping for a publisher once their next game is released.
I'm not sure if the japanese market will ever come around on the Xbox, but PC gaming is indeed on the rise there, and Microsoft could definitely establish itself as one of the bigger names there with Game Pass and a strong first party catalogue that appeals to people who aren't as well versed in western games.
Not sure how much that is worth for the company in general, it's not that big of a market in overall numbers, but when it comes to AA/AAA games, it's pretty safe to assume that whatever grabs that market will have pretty strong worldwide appeal. So working to have a stronger presence in Japan with the actual goal of being one of the major suppliers of that particular niche for global audiences doesn't sound too bad.