Fuel cell can almost double the thermal efficiency of combustion engine, while Liquid H2 has 1/3 the weight of gasoline, and with doubling the efficiency, the LH2 fuel will weigh 1/6 the weight of gasoline. LH2 can be stored in very light-weight aluminum container insulated by feather-weight polyurethane foam, so payload will nearly double, assuming that FC-e-motor powertrain will not weigh more than the existing piston engine currently in use.

So, LH2 will be very desirable for aviation just from the standpoint of payload gain and efficiency alone. The LH2 can be produced right at the aeroport from uderground H2 piping system and liquefied right at the point of consumption.

Good point, SJC.
One advantage of FC and E-motor is that they can be modular, of any sizes, and still retain the thermal efficiency, and cost effectiveness, unlike a gas turbine which loses a lot of efficiency in smaller sizes and cost more as well when having multiple turbines of smaller sizes, and a piston engine as well, which is not well balanced with fewer cylinders and costs more per hp with higher cylinder count. That's why we now see only twin engine jumbo jets, instead of 3-4-engine jets of yesteryear's. The engine count is reduced to improve efficiency and lower cost.

So, instead of having a single engine like in most small helicopters and private planes, you could have two or even 3 sets of FC, E-motor, and inverter, each running separately for backing up each other. You could also have 2-3 fuel tanks as well, in case 1 is leaking. With 3 separate power systems, if one should fail, you would still have 2 other running to provide 66% of maximum power, and will likely allow you to get to destination safely. This is better than a twin-engine plane or helicopter in which if 1 engine fail, you only have 50% power remaining, thus making continuation of the trip rather dicey, especially on a long-distance flight over inhospitable terrain and/or climate,

The harsh reality is that engine failures in single-engine airplanes regularly kill many people every year, and increasingly so due to more and more housing developments around small airports, thus leaving no place for ditching nor any room for miscalculation should engine failure occur.
So, with the eventual development of FC tech for general aviation, the FAA should BAN all single-engine airplanes and helicopters, because they are accidents waiting to happen and public hazard.