I think we'll end up with enough "next generation" energy (renewable, whatever), that we'll be able to afford the inefficiencies in manufacturing "legacy", high

I think we'll end up with enough "next generation" energy (renewable, whatever), that we'll be able to afford the inefficiencies in manufacturing "legacy", high-energy-density fuels -- and product precursors, e.g plastics -- where still needed. (Avoiding further extraction and all the pollution and environmental damage and unqualified and quantified future impacts.) And our overall carbon burden may be enough less (disregarding accumulated atmospheric load, in this arugment), that we can afford the corresponding limited amounts of exhaust. So, for common transport, I don't know whether pure hydrogen still fits in. It hasn't scaled, and it's still more difficult to handle.