the possiblity of having hydrogen powered GA aircraft in the future
Predicting anything -- especially the future -- is extremely difficult because many things stay unchanged for a longer time than we expect then suddenly there is a completely new technology that comes as a surprise.
I have an old book from the 1920s that assured readers that by 1950 everyone would have a personal aircraft in their garage and it would be powered by electricity sent by radio from the ground. We're still waiting. On the other hand when the C152 first came out could anyone have forecast that in 2009 we'd still be flying them?
The same technology developed for hydrogen powered cars could conceivably be adapted for GA aircraft, but this would mean also a new infrastructure for fuelling, new regulations and so on. Maybe before this happens electric propulsion really will develop in unexpected ways.