I'll be displaying my ignorance (and laziness) here, but these flex fuel engines are not designed to run on PURE ethanol, correct? They are still burning gas, right, with just a higher mixture of alcohol in the fuel? It was either in an environmental science class eons ago, or in the newspaper, that I read PURE alcohol burned in engines would require extensive engine mods. If so then y'all are just talking about forestalling the inevitable depletion of fossil fuels. Not that that is bad, but it doesn't actually solve the problem.
I don't see such radical change as the nat'l sales tax happening overnight. Congress is too chickensh!t to do anything that substantive. I can see a far more likely scenario of the sales tax being phased in and income taxes being phased out.
Unfortunately, I fear that in the inevitable temporary economic downturn, with federal tax revenue plummeting, they will decide they need to keep (or reinstate) the income tax, as well. In such a case (massive gov't shortfall) raising the sales tax would not be an option, as that would only further dampen recovery. Where's the cash gonna come from? Knowing gov't, any reserve will be spent and replaced with IOUs ala Social Security.