Regulation will make certain uses of AI illegal, and punishable. Just like murder is still possible despite being illegal, bit the law certainly helps in preventing murder by making clear that committing murder will have consequences.

The article you quote has 10 MJ/L as HHV for liquid hydrogen. This is at 20k and 1bar. You will need to account for the cooling device to give a realistic number for volumetric energy density.

4,5 MJ is at 690 bara, which i am confident to classify as very high pressure. Lower pressures are also used, and i’d say that this is in the same ballpark as batteries (in volume). This all follows from your article.

I’d say hydrogen fuelled aircraft are a one of the niches where the high volume and safety measures might prove practical, although hydrogen might also be used to form CH4 or longer C chains from CO2 and turned into a traditional but green fuel.

For home heating or transportation I don’t think hydrogen is very practical. But who knows. I hope i am proven wrong.

Energy density per weight, yes. Energy density per volume is about the same as a lithium ion battery. On top of that, hydrogen is difficult to store at length.

For this reason, hydrogen will remain an energy carrier in very specific niches, where large volumes are no problem and where the necessary safety precautions are acceptable.