There is no conspiracy keeping "hydrogen technology" under wraps. The only thing keeping electrolysis cells from becoming popular is the second law of thermodynamics, on top of really efficient modern engines.
Hydrogen cells only stand the possibility of working if they can decrease the amount of unburned hydrocarbons in your exhaust. Today's engines hardly have any unburned hydrocarbons in their exhaust... So how hydrogen can give great results by "improving" or "catalyzing" Diesel burn is beyond me.
Maybe hydrogen can work by increasing combustion temperature and burn speed, which would make the engine more efficient, but which companies don't do because of the NOx increases. Of course, if I wanted to do that, I would delete my EGR, advance my timing and cut out my catalytic converter...
Note that I'm not talking about cars running entirely off of hydrogen. Those are probably in the pipeline for the long term, and will really be getting their energy from the nuclear, solar, hydroelectric or fusion generator operating the electrolysis cell at the fill station. I'm talking about the people "running their engines off water" by having electrolysis cells in their conventional vehicles. Those people have streneous grasps on reality.