Ethonal and the various other alternatives, seem to me to be more correctly viewed as transition fuels to eaze the retirement of the legacy fleet of gasoline engined vehicles, and for applications where newer technology engines are either un-economic or not practical to develop, or for some other reasons.
It would seem quite obvious that a significant first order of reducing oil dependance in the US and most western economies, would be to target the usage of oil products in vehicles (cars, trucks, trains) that is currently 30% of US usage. Reduce that dependence and consumption significantly, ahd you have a bit of breathing room to work on replacment fuels and technologies in other critcal oil-dependent sectors (where it makes sense of course).
I would guess an expected country fleet retirement period would be of the order of 10 years or so, but could be accelerated by a change in road tax/vehicle registration and inspection policy to drmatically favour newer vehicles.
As far as I recall reading, for most of the various current crops that are candidates for ethanol conversion, a high water input is necessary to get high oil yields, although with cellulosic ethanol conversion this is probably not he so critical.
There still seem to be a number of issues regarding the actual economies of production (barrels input required for barrels output) that seem to have been submerged somewhat by the political expediency of swiftly introducing some ethanol based solution and by the rush of the various farming lobby groups to quickly realize a new and steady cash flow.
