They offer an electrically augmented version. One wonders if this could catch on in the US as a light duty, short range vehicle?
If you want to do something on your own in the US, Utah Trikes has a nice modified platform based on a commerical human powered tricycle. They can do custom work with a variety of transmission systems, augmented power and even custom work for a variety of rider sizes. I've never seen one, but know someone who is very pleased with some work they did on a new trike.