SMOKE, your assertion is factually incorrect. If one thoroughly reads the precedent link to the bill and projects its implications, one finds that the medical cannabis structure is still left intact. The two systems will exist simultaneously. Personally I am grudgingly supportive of I-502 for its general trajectory, while possessing an intense aversion to much of its structure.
It seems likely that the bill will provide a boon to the medical producers in the short-term, and perhaps even to the dispensaries before the new legal landscape is formed. Not only does it implement a new legal framework to purchase cannabis, it simply makes it legal for the average consumer irrespective of where the cannabis was obtained. Until a new landscape is formed, that will largely mean from the underground markets and the existing dispensary scene.
As far as growing is concerned, the medical sphere offers protections that the yet-to-be-prosecuted "legal" sphere does not, and I would rather operate under that aegis than under a system which will invariably be a target for federal prosecution. As the new legal structure strictly segregates the components of the industry, disallowing even an undefined "indirect" interest in another component, it seems likely that much of the production will also initially exist under pre-existing medical auspices until the federal government decides how they will pursue the issue. Even later it is likely there will be interdependence between the two markets in a new equilibrium.