Dinnerbone teased an image of a possible future enchant for 1.9 today, seen above. Two things seem to be suggested by the image: single-block thick ice might be more fragile in the future (though that isn't definitive), and it may be possible to enchant boots with some form of water-walking, by freezing the water into ice temporarily!
Being able to walk across rivers and oceans quickly is one obvious benefit of the theoretical enchant, but it potentially offers many more uses to map-makers looking to make puzzles out of the mechanic, as well as a sort of security function against monsters, who are not able to cross water easily (or at all, in the case of endermen). What sort of crazy uses can you think of for an enchant that can freeze water that you walk on?