In recent Nightshade Glen Cook releases (especially the first two Starfishers volumes), they list The Wrath of Kings as "forthcoming" and show it to contain Reap the East Wind, An Ill Fate Marshalling, and The Wrath of Kings. So it is still something they plan to release.

 

I expect the third Instrumentalities book in December or January, since the first one will be reissued in trade paperback in April, and the second one in August. My best guess is that the third and fourth Instrumentalities books will not ever see hardcover release, but are being formatted to sit on readers' shelves next to the Black Company and Dread Empire omnibuses.