I think this is why kayaks have probably pushed about as far as they can in the motorized direction (and in price) because one can buy a Gheenoe, a small model, and actually run it with a small outboard and go much faster, much farther, and get into really skinny water, stand in it all day, etc.
It'd be a really good vessel for fishing here in Texas, more of a skiff or boat than kayak . . . but a great idea.