Well, [url=http://www.games-workshop.com/en-GB/War-Zone-Damocles-Kauyon-EN]the rumours were half right...[/url]
There is a new Tau Codex, but it's an update to the current one, including all the new stuff we've seen over the past few weeks.
But in the link above? There's Kauyon. It's part Codex Update (so with the current edition and that you once again have all the rules), part Campaign Book.
Colour me intrigued...
Bit torn as to whether just get the updated Codex, or this one.