I bet someone will use a kite to pull them even faster, like a sail. That would be really fast, I've seen kite surfers travel as fast as some boats. How that would be possible to control, while swimming, I have no idea. I've heard that Benjamin Franklin invented an early flipper which was a board with a thumb hole, if a modern version (something like a glove with webbing between the fingers) were used in conjunction, that could definitely bring the speed up even more, and be one hell of a good arm workout with that added resistance. Though if the kite were used, the gloves would probably end up being used to steer the human torpedo.