Well yes and no. I can only offer conjecture. I do not doubt that there would certainely be a market for commercial marijuana how big a market would be difficult to determine. A big part of marijuana is its potency, it has been shown that marijuana actually grows better when the spectrum of light that reaches it is manipulated and enviroment richer in Co2. Other things like hydroponics, growing plants with no soil, have become very popular in marijuana horticulture. Its unclear if these types of methods would be viable in the type of large yield production that larger corporate entities prefer to be stream line and cost efficient because they require an extremely large controlled enviroment.
Like you mentioned a smaller produer like a co-op might be more efficient in managing the resource and turning a profit. I do think that this uncertainty does play into keeping marijuana illegal, but it is a smaller factor then the loss that big tobacco and alcohol manufacturer (who are the largest contributors to marijuana prohibition) would almost certainly take.