Sure there is..hydrogen infrastructure and building enough "hydrogen plants " to supply the fleet. then supplying those plants with enough energy to produce the hydrogen. There is also a problem with storing hydrogen in gaseous form. Its small enough to leak through almost any container.
I wonder how much "oil" ( ie energy) is used to make the hydrogen and transport it to market. Its a Law of Physics...you cant make energy therefore..you use more "oil" to make the hydrogen than what you will get from the hydrogen. ( if engine efficiencies are equal). Now if you can use wind, solar, hydro or nuke, then will remove the oil from the equation. Till then you have a hydrogen car still based off of "oil", only more of it than a straight burning "oil" car.