I believe kai waa (makers of the amazing vega surfski) make their outrigger canoe venturis that way. The Venturi cover is flat and the hull is recessed behind and under it. I am not sure why they do not do that on their skis but suspect it might have to do with the need to get center of gravity lower in a ski for balance. To do that the floor of the footwell and the outer hull have to be quite close together. With an outrigger balance seems to be not such a critical issue.
Current Skis: Epic v10 g3, NK 670 double, NK exrcize, Kai Wa’a Vega, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy