One factor to keep in mind is that ethanol use is not federally mandated at 10%. If it were then the current kerfuffle over the RFS would be meaningless. Producers would be required to maintain a 10% blend at all times. Instead, they have to blend the mandated amount, whatever that turns out to be.
Another thing to keep in mind is that ethanol is not the only oxygenate that can be used. So, if the 2014 RFS is set at 13B gallons, once they reach that amount they are free to source other oxygenates if they are cheaper. One of those is MTBE. While it's use is banned by most US states, it is still in use around the world. Whether it can be supplied cheaper than ethanol is another factor for the export market.
Clearly Big Oil continues to be driven by current profit rather than potential future liabilities associated with it's continued use.
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