Ghostcrawler (who decided to back off the forums, and then decided to back off that decision slightly) is now back on the forums with word of a change that Rogues will probably be intrigued by: he promises, in patch 3.3, a "change" to Vanish. That's about all we get, unfortunately -- some players assume that it's the Vanish fix they've been seeking for so long, but it sounds more to me like a reworking than a straight-out fix, considering that he points out that if Blizzard finds it's too much of a buff to Rogues (is he actually saying that Vanish working as intended is OP?) then they'll nerf it down.
Anyway, as for when we'll get to try it out, GC gives an official "soon (tm)," so look for a fix on a 3.3 PTR near you coming up quick. Hopefully they've come up with a solution that both keeps Rogues happy in terms of using Vanish the way it's intended, and also keeps the ability in line with other classes in the game.