The problem with hydrogen is that it is such a tiny molecule it'll leak through just about anything that isn't a dense material (think along the lines of the helium balloons that you get for birthday parties that rapidly deflate) so you have to completely re-think what you know about gas plumbing and storage.
As an example, regular inexpensive elastomers are completely useless for seals/hoses and have to be substituted for metal crush seals and hard plumbing which are much more expensive to buy, install (properly!) and maintain. The hydrogen will also eat into a lot of solid materials that you'd normally use for storage tanks (including inexpensive metals) and make them brittle over time, making it a challenge to store and transport safely without spending big bucks. When you also consider that hydrogen systems will need a belt and braces approach to detecting/preventing leaks and mitigation to prevent fireball explosions in a crash it's a big jump from existing fuel technology. Ultimately it's a massively expensive option and until it's equally expensive to use DERV I think it's going to remain a bit of a novelty.
