There are also practical engineering problems with making a "rolling coke/charcoal oven" reliable enough to last 250K miles with about the same maint as a gasoline car. There are certain economic balances that have to be achieved, if the maint cost is going to be X times a gas car maint and lifespan will be Y times shorter that has certain capital cost requirements which probably are not possible to meet.

Also this is something of an enviro-slur but renewable ideas are typically horribly polluting but the small scale types handwave past it. A gasoline engine can output exhaust cleaner in some ways than its input air, especially WRT hydrocarbons in smoggy areas, but a coke/charcoal oven is just beyond filthy polluting, which scales pretty well to one dude and his one car but is a non-starter for 100M American cars. The interstate would be unimaginable.

I believe the guy was only using what was available around him. Oak apparently provided the best bang.

Who knows what else that we could use that would scale.