the inflateable sail is also known as a double surfaced sail. it's the standard in hanggliding. i had a friend that studied the Macharje(spelling?) book on aerodynamics and developed a double surface sail for windsurfing. he produced quite a few, but no bigshots ever adopted them and won a big race. i used them for a while, but never got dialed in enough to prove they were better than a regular camber induced sail. it would be hard to make one that could be hoisted like a regular sail, but there is potential in the idea.