It is my understanding that even at 10,000 psi, hydrogen is still a gas. Using liquid hydrogen is problematic since you need a heat source to convert it to gas, so i don't think that is even prefferred. It is also my understanding that the tanks are available and safe (carbon fiber wound alluminum) you can do well with 5000 psi tanks too. And hydrogen embrittlement (as far as i know) requires heat. If i sound optimistic, it's because i have ben researching hydrogen and the advantages are enourmous. I know from my personal experience that nothing is ever really accomplished by pessimists, so i'm taking the enthusiastic route.