As with the previous two games, Dark Souls 3 will have its art and design catalogued in a Design Works book. FromSoftware have confirmed the Japanese release on their twitter account.
If publication follows the same process as the previous two Design Works books, then Udon Entertainment will release an English translation a few months after the Japanese one comes out. That’s primarily of interest for the extensive and enlightening interview with FromSoftware designers that has appeared in both of the prior releases. Hopefully the Dark Souls 3 book has one too.
In Japan, the book will be released on 31 March and priced at 3,500 yen. Since it’ll be out after the final piece of DLC, we can presume that it will include art pieces from those add-ons.