I´ve been experimenting with the technique. It takes a considerable amount of skill and practice to get the timing right in tacks. If you wait too long to get the rudder up, the side loading makes it almost impossible.
It makes sense when you have a long tack in big air where you´re footing. If you stall out the boat by feathering in the gusts, you´re screwed.
The reason you haven´t seen it that much at the 16 worlds is that there aren´t that many pictures up yet and because the waves are so big relative to the wind. I saw a lot of people using the technique out on the water yesterday.
In the first race yesterday, I was doing it, but mainly because I was having rudder problems and the boat was driving better with one rudder up.