RE: Cutouts - fact or fashion
Knowing how and why is best, period. It may not be necessary, but it can also save lots of time and energies. I think that knowledge of physical facts that are behind board performance is even more useful than models, due to the high degree of subjectivity and the complexity of our sport.
that is what I was saying: IMHO a superwide tail with no cutouts is the most efficient, and the need for cutouts is more related to longitudinal stability than else. As for the irregular surface, it should not be a problem as the trailing edge of a cutout would behave just like a tail's trailing edge. Only, I guess the angulation between centerline and the side of the central portion of the hull (the one between the cutouts) could be critical as it could not have a sharp release and therefore generate turbulence and drag.
I agree about the idea that proto testing is probably the best way to go, both economically and practically. One can get new ideas even from a screwed up proto, plus I don't think there can be a sophisticated and complete enough model for numeric simulation of a sailboard (+ rig + sailor) hull's behaviour. This makes clear ideas about the physics even more important.