The Mustang E is selling well here in the UK. It has just completed a Lands End to John-o-Groats efficiency run and broken a previous record set by a Tesla.
A friend was telling me last week that the Ministry Of Transport here has put a stop to further development on Hydrogen cars as they can't work out the road tax cost for owning one yet, that's been on hold for nearly ten years!
Gas conversions, not petrol to us but gas, are popular for those with big cars, Range Rover etc, as per litre that is still only 35pence. The tanks is a pressurised cylinder and normally in the boot/trunk space. The cars have to stay as fundamentally a petrol powered vehicle with the gas as a backup fuel source.