Various US manufacturers and a couple of government agencies began talking about hydrogen powered vehicles at about the same time (ie 20-25 years ago, but as in Australia nothing came of it, at least not as far as commercial applications go.
My understanding is that the infrastructure needed was the main practical/mechanical obstacle. The hydrogen generating centers, the transportation network, and the local storage facilities, and the refueling systems, were all doable to a degree, but the cost was not compatible with where we were at the time. In effect, there would have to be hydrogen cracking planes/suppliers, transporters, and end refueling stations, that would all have to be run on speculation (economically) to get it going. The only serious practical/mechanical obstacles that I am aware of were the transportation, and local storage/refueling and refueling system safety concern.
The other obstacle was/is the oil lobby.
It will be interesting to see if Japan can do it.
Question for Shinpachi:
In Japan is there anything similar to the oil lobby here in the US?