Wouldn't aircraft H2 storage just be low pressure insulated tanks that self maintain their temperature by the boiling of the H2? Insulation is mostly air and as a result is light.
Any vented excess H2 isn't a big issue. You can just dump it straight into the atmosphere with no environmental consequence. If that turns out to be unsafe in some situations you can run it through some sort of heated auto lighting burner.
The energy loss of liquefaction is worse than that of methanization. If you add liquefaction of methane it gets close and H2 might even be slightly ahead, but LNG handling would be so much easier. 190K and 33K are very different temperatures.
Any vented excess H2 isn't a big issue. You can just dump it straight into the atmosphere with no environmental consequence. If that turns out to be unsafe in some situations you can run it through some sort of heated auto lighting burner.