Classic cars are much easier to convert to electric than hydrogen. I’m not even sure anyone would make a kit to do it. There’s just so much complexity with fuel cells.

Well I agree with your other comment, but about this one, retrofitting (ICE->EV) is a thing. Even if very niche for now.

Used Prius is always free and used Tesla is cheaper than a conversion. It never will make sense except for few classic cars.

With the way cars are built today it can be an endeavor to change a lightbulb, let alone the entire propulsion system.

It is niche but growing less so by the day as conversion kits mature and more options make it onto market.