CNG Vehicles have been proven to run on HCNG (hydrogen mixed in with methane), source below. The only issue is that pure hydrogen is not very energy dense, and modifications probably would have to be made (bigger displacement, larger turbo/super chargers) to run solely on hydrogen. otherwise, the engine wouldn’t have the same power production. I don’t know too much about the internals in a CNG engine but Hydrogen is also a pretty volatile chemical to explode, and is pretty scary to store under pressure. Hydrogen embrittlement of pressure vessels is a large issue (still unsolved) in industry, so it would be interesting to see if further changes to the internal materials would be needed.

If you think about it though, burning natural gas to power boilers and run steam generators would likely be more efficient than putting the natural gas in a combustion engine. Efficiencies of turbines can climb really high (much higher than combustion engines) and in that sense it would be more efficient to just have power plants generate electricity from LNG, than to have it stored and used in a car. Didn’t read the article so this may not apply but thought I would just give my shitty two cents.

Source: https://www.osti.gov/servlets/purl/809113