It's pretty simple but complicated at the same time. If you look at nature, nature has figured out a way to degrade wood. If we didn't have that, we'd have wood up to our ears and above. It does that in a very slow process. It takes a long time to decay a piece of wood, and when it does that, it doesn't produce anything of value; it produces CO2.
We know what the organisms, enzymes, and individual parts of that process of degradation are and we can capture them. The problem there is to bring all these pieces together to degrade the cellulose and once you degrade the cellulose to simple sugars, like table sugar, to turn that into a fuel or a chemical.
We know how to do this. Now all we have to do is beat petroleum. It's really an efficiency problem, not a process problem.