That is what will kill H powered vehicles, infrastructure. Stop at nearly any major intersection and count the gas station signs you can see. Now think how much time/$$$ it will take to retrofit that installed base w/ H capabilities. While I think it is a great idea, they (here we go w/ THEY again! /forums/images/graemlins/grin.gif) need to think past the vehicle and work on getting infrastructure in place to service/refuel these vehicles. I remember back in the mid 70's everyone around here was going to go to LPGas. But you could only fill up at a couple places. And on a cross country trip you had to find RV parks that MIGHT have a tank, but they were set up to service 5-10 gallon bottles for RVs, not lines of automotive traffic.
I drove a diesel p/u in college. I had to drive several miles to a truck stop (in Dallas/Ft. Worth) to get diesel. Thankfully diesel is more common today but it is the same deal w/ H, or biodiesel, or propane. If they(again with the mysterious THEY) design a car to run on Windex, you still need somewhere to fill it up.
Sorry, didn't mean to get a soapbox. But I think we may be attacking this from the wrong end.