Not so fast. Hydrogen storage is a major problem requiring tanks containing 5000+ psi to hold enough to have any kind of decent range. Filling stations won't allow drunk, ignorant, and careless owners to operate the dangerous connections required, so tank swapping is required. Oil used to lubricate any of these engines will burn in small amounts at each cycle, and that small quantity nowdays will require downstream processing via catalytic converters (please don't call it a cadillac converter, that is so ridiculous). Plus oxides of nitrogen 'pollution' is also produced by the high flame temperatures, so we're back to EGR feedback to kill the efficiency. The government has not banned nitrogen in our air, (yet).
On the good side, any tank rupture resulting in a fire will see flames going straight up because it's so much lighter than air. That's important for EMS & fire teams. Crashes are still unavoidable.
Carbon atoms are the core element of the highest density fuels because they store so much energy in their covalent bonds. Ever wonder why people are essentially carbon based ? Nature lalways selects the easiest, simplest, and most efficient systems. Silicone based people are kinda rare in the universe unless the air temperature is like that of Jupiter's moons.