Right, the first thing to always remember when you're doing a hybrid is that you're stating up-front, "I want to have two engines in this machine -- that's a weight and space cost that I want to pay up-front." As mentioned by the article, with airplanes when you increase weight everything has to get bigger to accommodate it. That doesn't make it impossible, but does make it a bit tricky.

Another interesting question: the fuel cell design in the original post is probably not reversible, is it? It would be really cool if given 10-20 more years of work we then used variable-pitch propellers with reversible fuel cells allowing for a plane which, during descent, could regenerate most of the energy used to make its ascent. It might also make pilots less worried about limited range, because they'd know that in a pinch they could get some more energy to the battery.