In our opinion a single cam is not doing enough to make it very viable. Sticking a single cam in a bad sail will not make it better. Taking it out of a bad sail will not make it better. There are a lot of elements that work together to make a sail work well. There are some pretty good single cam sails on the market.
People like to talk about the weight of sails, whether they are heavy or light.
There is a big difference between physical weight and apparent weight. A lighter sail may actually have a heavier feel due to it's design and how it is rigged. For sure a huge difference in weight will be felt, but overall performance will not be changed with a small difference in rig weight. A good balance of materials will allow a reasonable weight in a package that will last. Windsurfing board designers seem to be a tight-knit community who discuss their thoughts and ideas of designs.