Rather than mess around with hydrogen, with the proper mandates a lot of jets could switch over to renewable jet fuel. One of the main leaders here is, surprisingly, the US Navy: http://www.altenergy.org/new_energy/seawater-into-jet-fuel.h... directly from seawater and nuclear energy from a ship's reactor, or various other biofuel initiatives.
The Navy does a lot of this. They funded a program to make biofuels from algae.
But don't forget that the stated purpose of funded research is often a lie[0] and this is not necessarily viable outside the lab.
[0] You get other benefits from the research including subsidizing your national industry, training your workforce, doing research you're interested in with a more politically palpable purpose.
