I love the idea of a waterproof phone, but i don't know if i would want it enough to have to deal with the covers on all of the ports (i ripped off the cover for the charging port on my DNA.) The Sony xperia z is dust and waterproof, but the back of the phone is still glass coated, so you still don't get any fall protection. I would love a phone with the same rubbery back as my nexus 7 though.
I would keep an eye on Motorola's next generation of phones to do something like this. Larry Page made a comment about phones not breaking when you drop them in his recent earnings conference call (i believe he was discussing what Motorola has been up to.) I'm really excited to see what their next line of phones has to offer.