This seems like a good working solution to a long-running problem. However, I feel that it is important that rules such as those proposed are confined to food crops only, and not extended to ornamentals (which are currently covered by the same patent and plant variety rights legislation). Additionally, who defines what is or is not an "exempt" farm?
Having said that, I’ve always felt that it is bad practice (i.e. unethical) to take plant patents/PVR on naturally occuring plant varieties where no development work has taken place. Where there has been a selection or breeding process undertaken by a plant breeder/developer, then that is a different matter, as there has been cost and effort incurred which needs to be recouped and profit sought. This is not the case with plant materials that occur naturally in the wild (although defining that state will always be open to conjecture).
separating the wanted from the unwanted