I don't think the dagger board insert is quite the same as the K15. That was a windsurfing slot in the middle of the board. In this new board, it's a fin box just forward of the regular fin box. Otherwise, it certainly has a good deal of K15 DNA.
Interesting that Starboard has resisted making an Unlimited downwind board all these years, and when they finally do release an Unlimited, it is a flat water rocket. Still, I'd love to take it for an extended run.