I'm curious about what the salt water turns into after it's lost a bunch of hydrogen atoms. Hydroxyl (OH) is apparently not the best substance to have around, and you have a bunch of Na and Cl sitting around from the salt. Then there's the question of how much energy you need to pump into it to keep the reaction going. Also, at what rate the water can be forced to emit hydrogen, and for what duration per unit volume before becoming exhausted.