The proof for the paperback of The Ravening Deep arrived today, and it was absolutely fine. A few clicks later and it started populating on the Amazon store!
It's now available from all the usual regional Amazon sites, although on the France, Italy, and Spain sites it says — at time of writing — "temporarily out of stock". That message usually vanishes within an hour or two.
Because it's a whopping 542 pages, this volume is the most expensive yet in paper. What I'd suggest is waiting for a bit if price is an issue for you, because Amazon applied their own discounts to the previous two volumes for no apparent reason.
As with the other volumes there will be a compressed edition coming at some point, which will be made cheaper by sacrificing the nice font size and comfortable feel of the larger book.
All store links are now on the book page.