Awesome
If you had the mast a bit rear from the wing, and the wing was designed with an "S" profile (maybe even washout and swept back) - then it could be really stable without a rear wing (not requiring a better rider).
BUT, I believe, as in airplanes/gliders, that the cost is bigger than the benefits - so the performance will be worse indeed
Althoug, it could be really easy and simple with such a device - nothing you can hurt your feets on, nothing that can hit the bottom when low water, no "difficult" fuselage to build
Peter
PS:Denise, I thought the very same - I always ride barefooted, except when heavy winther, but I am quite sure the bottom close to is as the beach on the video, so tough call for him