I agree with you on the part about not being emission free because currently we do get out hydrogen from fossil fuels. Yet the storing of hydrogen storage in cars I disagree with. BMW has made a hydrogen powered combustion engine. Not a fuel cell, but it actually burns the hydrogen making water. They store liquid hydrogen in a tank behind the seat. They crash tested the tank and it is VERY strong. They dropped a full tank from a ridiculous hight and it didn't rupture. I read it on the BMW site. Also hydrogen has to be in certain proportions with O2 to be combustible, or so I am told. Is that wrong?
Basically, the real question is "can you make the tank strong enough without it weighing too much?" Back in the 70's when they produced the SR-71 Blackbird (that big, long, flat black plane with huge engines capable of reaching over Mach 3), they rejected hydrogen as a fuel because of the possibility of explosion. However, a) it was in an airplane, therefore had much narrower weight restrictions and b) it was long before modern composite materials.
Now, with composites, BMW could do it easily, but composites are not simple to make. Metal you just pour in a mold, but for woven-fiber composites (the best kind), hand assembly is still required for the vast majority of applications (I've actually worked doing so once). So the question is, "can they make enough of them at reasonable cost"?
Finally, there's another problem with composites, which is delamination. Because there are numerous layers, failures can occur by the layers separating. This is exacerbated by extreme temperatures (heat or the extreme cold of liquid or compressed hydrogen) and simple duration.
Maybe I'm not giving them enough credit, but I would only trust it if they loaded with H2, unloaded it, repeated the cycle a good 100,000 times (nothing that can't be done via machine in a few weeks), filled it again, *then* dropped it.
It's not impossible, but with alternatives such as batteries, metal hydrides, and compressed air, I'm skeptical of whether it's worth the bother.
Mokele