[alephnil]

In fact it is so mature that what we today call biofuels was what e.g Rudolf Diesel envisioned that his engines would run on, and the prototypes used for fuel. (He also thought of coal dust)

The problem is not the fuel itself, but the possibility to scale up production. Petroleum is available in vast quantities compared to all biofuel feedstocks. Most biofuels today compete with food production, or are not very developed, like cellulose. Even cellulose would have a hard time scale to the sufficient quantities if all the technical problems were solved.