At least there are some cost numbers here that can be argued. I have long argued that the main problem with hydrogen is storage.
If you could make the infrastructure supporting petroleum disappear overnight and then consider the cost of reinventing and rebuilding it -- it would seem imposible. So I'm skeptical of hydrogen, but still interested.
It can't/won't happen instantly. Gas stations spread from the larger cities outward gradualy. I'm sure that could be done again with the right incentive. The real problem is the clean up of the former gas station sites.