While I recognize your "Coke" or "KFC" analogy, I think that a better one in this instance would be that of Monsanto which sells Round-Up Ready Seed (corn, soybean, etc.). They make quite a bit of money selling their genetically altered seed and police it carefully. The owners of the Simcoe patent could price their product accordingly and sell the rhizomes to those interested (which is a small number anyways).
At some point some enterprising company/individual will be able to breed/cross breed a Simcoe clone or will come up with something superior and the point will be moot. Montanaandy