Hydrogen fuel cells are still way too dangerous, as are supercapacitors. The SC's are also plagued with rapid degradation and density problems.
I'd LOVE to see a safe hydrogen fuel cell, that's ideal. And I agree, it's only a matter of time before someone figures something out. In the mean time, they are making huge strides on the rest of the tech which is great. By the time the power source is figured out, maybe they'll be flying. haha