As announced during a recent livestream, Dragon Quest XII is currently "in preparation" by Yuji Horii and Yuu Miyake at Square Enix. This is the same livestream that revealed the existence of Dragon Quest Walk, a location-based smartphone game. The stream also showed off Dragon Quest XI S, a Switch port of Dragon Quest XI, the upcoming Dragon Quest: Your Story movie, and a new expansion for Dragon Quest X. Many of these announcements were not new, other than the discussion of Dragon Quest XII and Dragon Quest Walk.
From the brief discussion between Minase and Horii, Dragon Quest XII seems to be in the very early stages of development. The pair have yet to decide on the focus of the next Dragon Quest, let alone start production. Considering that Dragon Quest XI released in mid-2017 in Japan and worldwide in September 2018, it could easily be another three to four years before Dragon Quest XII makes an appearance. No matter the case, don't expect to see Dragon Quest XII any time soon.
If you're in dire need of more Dragon Quest in your life, then fear not. The rest of the world is getting their chance to check out Dragon Quest Builders 2 when it releases on July 12th next month. Furthermore, a new Dragon Quest Monsters game is set to come sometime in the near future. With E3 just around the corner, and considering the new Dragon Quest Monsters game stars two of the protagonists of Dragon Quest XI, we could see more of the brand-new Monsters game in short order. If not, considering Dragon Quest's enduring appeal in Japan, it might not show up again until Tokyo Game Show this fall. In any case, Dragon Quest looks to continue its RPG legacy sometime in the future with Dragon Quest XII.