Thanks to all who contributed to answer my Q. I am left (distinctly) unmoved and - given that if Israel’s Eviation (in the form of the Alice) is to be believed - a 400+ mile-range battery-powered commuter aircraft is already feasible, and given that that is a quarter of the global aviation market, all this amazing (and amazingly complex and expensive) technology is going to be simply left behind by the incredibly rapid advances in battery technology (along with equally complex, expensive and impractical hydrogen).
What short haul airline is gong to want all this engineering complexity when an e-plane has 1/10th the down time due to servicing needs compared to turbine-based aircraft, not to mention the cost (nor the cost of the ‘fuel’)?
In the short term, short-haul aviation will transition quite quickly to battery electric just as road-going vehicles are, leaving long haul to ever more expensive (due to the drop in demand) kerosene. Even this would achieve a dramatic cut is emissions from aviation, enough I would think to keep the tree-huggers happy (as long as they continue to have to balance their conscience with the desire for a sunny holiday once a year).
As for the long terms and medium distance air travel? Well, there’s dirigibles… and long haul, near space…