When FINAL FANTASY XIV: REALM REBORN was released in 2013 as a renovated version of the original edition, only PlayStation owners could enjoy the large MMORPG (Massively Multiplayer Online Role Playing Game). The reason provided for the exclusivity was due to Microsoft's ability to handle support and issues on the Xbox One in the past, specifically for such a huge online game.
Final Fantasy XIV is about to have another expansion added under its wing, namely Stormblood. Director Naoki Yoshida was asked in a recent interview whether it will be available cross-platform:
We want as many players joining Final Fantasy XIV as possible. We need to make sure Nintendo and Microsoft understand what we do and have them know about our online and QA regulations. We believe these conversations will take a long time.
He also believes that expanding the community and providing support to them should be a joint responsibility between Square Enix, Microsoft and Nintendo, much like Sony and PlayStation had done. Yoshida does not believe that Nintendo nor Microsoft will be able to resolve these matters any time soon.
In the meantime, you can watch the trailer for it here: