Cool engine.
Seems to have more than a few potential stress points that may fail.
I think the near future, using existing technology, is Nat GAS. It works. If Auto Makers get behind a “Passenger car” version, you’ll be able to swap out a tank (just like your gas grill).
Demand vs. Supply, the chicken and egg paradox of building the vehicle before having the proper filling stations.
The tank on most gas grills holds 4 gallons of L P Gas.
There were a number of propane cars running around in Canada ~20-30 years ago.