Several universities - and several private companies and joint ventures - are working on producing “green crude” from algae. Since this would be a direct replacement for crude oil from petroleum, it seems to me to be the most likely new feedstock if the cost can be brought down. And it might be the best way to capture sunlight in usable form, as well as a way to recycle CO2 from industrial processes.
I would like to see much more R & D in ths area than on new ethanol feedstocks. All of the petroleum that we have found and extracted so far has been derived from prehistoric algae beds, so this would be just a shortcut to the original source.
And if we really need an ethanol replacement, butanol is a far better oxygenator.
Cellulosic ethanol from wood is not yet perfected, but would be a great product. It would provide a market for biomass from thinnings in our overstocked and choked National Forests. This would help to offset the costs the American public is now paying for either fuel reduction or firefighting. I know that more than 200,000 acres burned this past summer in my county alone. Would have been better if it went into our tanks than to have all that carbon released into the air.