You're not wrong but "can you make hose X with material Y" or "can I get valve body P with spring rate Q" is a hell of a lot better than "we need custom hoses" or "is this casting good to 10kpsi?".

The big problem with hydrogen is just how small it is. It likes to leach through stuff hold just about everything else. You very well might need custom hoses, custom seals, and custom materials for the castings just to safely store it at 10kpsi. It'll leak through solid steel containers that will otherwise hold helium fine.

Even worse than simply leaking, hydrogen can diffuse into the crystal structure of metals and cause havoc with the material properties. It's definitely not as friendly as hydraulic oil.

Exactly. This is a major problem with anything hydrogen related, especially if it has an expected lifespan of a decade+.

And once it gets the thing all brittle and it starts leaking, you won't see it burn as it produces a lot of IR but almost no visible light.