but I don't see this supplanting the fossil fuels any time soon
Maybe yes, maybe no. We're probably going to continue using liquid fuels for a long time. Some folks talk about the hydrogen economy being the replacement for hydrocarbons, but I've often wondered why. Hydrogen is a tricky fuel, starting from its relatively inefficient creation, through the difficulties in storage, transportation, distribution, to tricky bit of transferring and storing it in a vehicle tor provide sufficient usable range. If you've got the technology for manufacturing huge quantities of hydrogen, why not go one step further and create low weight hydrocarbons (methane, ethane, etc)? Those are much more energy dense, easier to transport and store, and there's already an extensive infrastructure in place.