All together very good ideas of Michel to reduce drag. Of course surface design is the secret of nature. But first the main issues have to be solved. Main part in limiting the speed in windsurfing is the ratio between board and sail. See the kiters and you will find for speed kiting a 9 sqm kite and a very small board with moreless no fin. Additional a fast going kitebord is extremly reduceing the wetted surface. Because of the big kite and small board speed kiter have to go very deep downwind to find the balance between kiteforce and bodyweight.
Okay, conclusions for speed windsurfing:
Use a big deep fat sail, much bigger as usual recommended for your speed board. Very difficult to start but needed for the deep downwind. Next problem to solve: When reaching 80% of your top speed the fin is much to big! That means the fin is not anymore working in the field of best drag/lift ratio (polardiagram). Best would be to be able to reduce at 80% top speed the size of your speedboard down the size of a mono water ski and also reduce the area of the fin to the size needed at top speed (can be calculated by finding the are out of the best drag/lift coeffizient). A lot of points to solve to hold against the top speed of kiters.
But: I all conditions with micro waves bigger than a view cm windsurfers will be faster. Only in "pools" of extremly flat water and deeps of a view centimeter allowing no waves kiter will be faster because of there physical advantages.