Last month, evidently, as detailed here. Almost 200 pages. I could joke about what could be in the book, since the game really seemed to be kinda hurting in the art budget in the beginning there, but: I doubt they'd release a big expensive artbook three years after the game's release if Luminarise sunk. Koei's been looking for ways to revitalize the franchise after Étoile; it seems that this one might have stuck.
Also, evidently, they're holding some 30th anniversary events in January. Wonder if any sequel announcements are on the horizon.
