Atlus would be pretty big in terms of trying to get more penetration in the Japanese market. Heck, it'd help even in Western markets. Persona 5 was pretty big this generation and generated a fair bit of sales for the PS4.
Even if it's only to get some titles to be multi-platform, MS would likely consider that a win. This goes for other Sega IPs as well. Making new entries in the Yakuza series day and date on Xbox along with PlayStation would be a win, for example.
Relic is already making an exclusive title for MS (Age of Empires 4).
Creative Assembly focuses heavily on PC as their core series doesn't translate well to console controllers. Creative Assembly has also made one exclusive for MS in the past (Halo Wars 2).
Phantasy Star Online 2 (the largest MMO in Japan), is currently Xbox exclusive outside of Japan due to MS paying to have it ported as well as paying for translations to other languages than Japanese. A Non-JP PC version will be coming later.
Basically Sega are no strangers to working with MS. Phil Spencer has been working to make that relationship stronger as there are still key franchises that have been PlayStation exclusive due to development costs and market penetration (many, like Yakuza are kind of niche).
Regards,
SB