Once the hydrogen generation problem is sorted out, the remaining problem is that these fuel cell engines need a part made with platinum to work. There isn't enough platinum on the planet to replace every gasoline engine wih a fuel cell engine.... However, I seem to remember reading recently about research into using some sort of silver alloy instead. Or something.
And I think the "artificial engine noise" idea is just too silly. Sure, here we have a near-miraculous engine that also happens to reduce noise pollution as well as other kinds, so let's just deliberately add noise pollution back in? No way...how about people look both ways before crossing a street, instead....
--Eric