I really doubt it. From what I've seen, the only mentions of a WD release have been from people randomly speculating.
Also, GW can't be THAT cruel, can they? They know we've been waiting for a new codex for a long time and are desperately in need of one. SoB are a fairly unpopular army, so they could get away with a WD army list with not too much complaint, but Tau (despite being one of the oldest codecies) is still a reasonably popular army. Their will be a few unhappy customers if GW gave that sort of treatment to Tau. Unforunately, I wouldn't put it completely past them.