While nice in theory, it'll be bad for business for public swimming pools. Think of how many young kids are in the pool (under 3 years of age). Whether you like it or not, there's pee in the pool.
They also, contrary to GP, are not at all intended to control urine release, only feces.
Also, how many dirty assholes are getting cleaned by the pool water? That dude that was just grunting in the stall of the locker room likely didn't wash his ass before jumping in.
Makes sense, not sure why other countries don't do the same. I'd much prefer fewer chemicals in the water and a required shower than the current system in the US.
Swim diapers are to prevent feces from getting in the pool, or at least greatly limit the quantity. They really don't do much of anything for urine, nor are they intended to. (An absorbent diaper in a pool would be useless and fail completely as it would become oversaturated.)