I'm skeptical about something with capability for explosive decompression getting approved by the FAA without a serious (meaning heavy) protection system around it. Oxygen containers are heavy, and it isn't the air providing the weight.
The other challenge I can see from a weight standpoint is that the ideal shape for the 'fuel tank' would be spherical ( maximum volume with minimum surface area ), but spherical doesn't 'fit' well with current airframe shapes in my mind's eye. Long and skinny ( e.g. wing tanks ) is about the worst shape from a surface area perspective. Still, I saw Honda's doing a US hydrogen car pilot program, and I would have thought of similar challenges for getting auto approval. So perhaps I'm just too skeptical. http://automobiles.honda.com/fcx-clarity/how-fcx-works.aspx
