Two main hurdles stand in the way of mass production and widespread consumer adoption of hydrogen «fuel cell» vehicles: the still high cost of producing fuel cells, and the lack of a hydrogen refueling network.
The mainhurdle with adding downloadable content to a title like The Elder Scrolls V: Skyrim is that the main game is so substantial, that any post-release add - ons need to add something new to the mix in order to stand out.