RE: Cutouts - fact or fashion
Although I do not know much about hydrodynamics IMHO, the main target for cut outs is to improve control at high speed and reduce drag since both are related. Reduced drag might also help in putting a hull on a plane earleir...maybe.
Obviously it will depend on a correct design for it to work properly. It might even improve or change slightly the way a given fin works.
The idea of setting different possible depths sounds good however in the real world I believe it might be not very practical.
This subject seems to me a good application for fluid dynamic softwares. I do not know if they're in use in the windsurfing industry but I know from expeirence that some time should be spent to validate it ( in that applicatin ) otherwise results would be meaningless.
My two cents.