I don't know what took so long. It's just so obvious, you know? A swimming pool that doubles as, wait for it...a floor. Tired of swimming? Feel like walking? Then you need the Hydrofloor.
Basically, the pool's floor slowly moves up and down, either up to ground level (where it's indistinguishable from the surrounding patio) or down, forming a more traditional pool. The best part might be the stairs--they retract from typical stairs into a kind of grooved flat surface.
The pool fills up with water as the ground lowers, meaning it's already filled with water even if it's sitting at ground level. Apparently that keeps energy costs lower as well, since it retains heat rather than requiring a separate heating time before use. The depth of the pool is adjustable, making it kind of a fun solution for incredibly rich people with kids, but a terrible solution for careless and/or blind divers. For a price, you've gotta contact Hydrofloors, the manufacturer, but you can rest easy: you can't afford it.