Your other points hold, but I don't think this one is necessarily so (depending what you mean by "a while"): electrolysis is so incredibly trivial that I suspect it'll become green as fast as the grid in general, and if current exponential trend continues, that's going to be almost everything within a decade.
If the current exponential continues. It might, but such is never assured.
Just doing the simple math of the twh needed to produce the fuel for a major airport on a daily basis is kind of eye watering. Just a little back of the envelope math makes it really obvious that that's not going to be a thing any time soon even if we do get some magic laws of physics defying electrolysis technology (those pesky laws of thermodynamics are hard to beat though).
And even just shifting current hydrogen production, which is good for a few percent of carbon emissions today, is a huge undertaking. I agree that electrolysis improvements will actually make that cost effective to do at some point. Possibly even as soon as next decade. But right now it just isn't and most of those electrolysis companies still have a few things to prove. Like having working products or the ability to produce those cost effectively at scale. Either way, within now and a decade, we won't have nearly enough renewables in place to power any of this new hydrogen economy. We'd struggle to power the current one with that. As long as renewables remain scarce, hydrogen is not a great use case for wasting them.
Yes. 30% per year compound growth does that very quickly.
(Exponentials will turn into s-curves of course, no guarantees, but growth here doesn't have to be asymptotic to the current market).
Blended wing body designs may solve the volume problem. It's only intractable if you try to fit the same energy content into a modern airliner that was designed for Jet A.
Weight is the usual suspect in aerospace, and fuel weight significantly favors hydrogen over Jet A (factor of ~2), so a blended wing body design with a much larger internal volume wouldn't even have to have equal aerodynamic efficiency in order to be a suitable replacement.
To be clear, this is not a simple shift and will probably take decades, but it is merely an engineering challenge rather than a fundamental constraint.
Green steel you can do without hydrogen. Basically you need lots of heat and some carbon to produce steel. Generating heat with electricity is not that hard. You can use induction, plasma heating, resistive heating, etc. And doing that is a lot more efficient than using that same electricity to first create hydrogen and then burn it.
Hydrogen has its place, mostly as a chemical half product that is used to create other stuff. It doesn't store very well; it doesn't travel very well. It's mostly used close to where it is generated. Which as of yet is done almost exclusively by expending large amounts of fossil methane or coal. Green hydrogen production is minuscule and relatively inefficient and costly. Most uses of hydrogen today are neither green nor sustainable. Or carbon free. And that's going to stay like this for a while. Even just shifting current hydrogen production to being green is going to take a massive investment and take decades.