As is current with GW PR they released another one of their "teaser" trailers today. The trailer is really just close up shots of parts of the Riptide and a few phrases. At the end of the video is the date 30.3.2012. Which lends itself to being the Tau announcement as the releases is supposed to be on the 6th of April which would conform with the one week preorders GW is going with making the 30th the one week before date.
[url]http://www.youtube.com/watch?v=Ug0aw5gRPkw&feature=player_embedded[/url]