So I already knew about this from before, but one thing I never understood was instead of banning it outright, why not just put in a rule that says your futures are invalid if you control X percent of the underlying asset?
In many ways, it's easier enforcement-wise to just ban the thing, especially if you don't think it's actually important to have in the first place.
Another possibility might be something like a tax on hoarding large amounts of food e.g., each day it sits around without being sold or consumed past some grace period like one year. Maybe only tax profits achieved by hoarding food, similar to long term versus short term capital gains, unless you sell after a crop failure.