Not saying this confirms anything as it looks like information we already know, so I'd would wait for an official announcement before getting too excited. But IGN Spain picked up the story for what it's worth. Seems like they may have put in for an official comment from the publisher, if I understand correctly. This might add a little credibility to this rumor. At the very least, maybe they'll receive confirmation, "yes, no, or not at this time".
http://es.ign.com/ni-no-kuni-2-ps4/124588/news/ni-no-kuni-2-llegara-a-xbox-one-solo-en-digital
Full article translated to English:
"It seems that the alleged leak of Ni No Kuni II: The Rebirth of a Kingdom as part of the catalog for Xbox One was very accurate. The media specialist Xbox Generation points out that several sources of Bandai Namco claim that this JRPG will release for the Microsoft console. However, it will only be in digital format.
This version, with no official release date, does not appear to have a physical edition except in the United Kingdom, pending the distributor to comment on it.
The Level 5 game is a beautiful JRPG with the aesthetic of Studio Ghibli, who actively collaborated in the first game, for Nintendo 3DS and PlayStation 3. However, the studio does not appear in the credits of the second installment due to the closure of its production department and the change in its business model.
Ni No Kuni II will be released in January 2018 , being one of the most anticipated titles, and a very good way to start the year. Let's hope that Xbox users do not have to wait too long to enjoy it."