Clever, but I don't think I would have much use for such a key float. Just before I launch I stash my car and trailer keys in a sealed Zip-Loc that goes in the Hobie bag in my forward hatch, I also keep a spare set of car keys on a standard foam float in my seat back. Course, if I get separated from my boat, then I'm in key trouble, but I think that might be the least of my worries at that point. I use cell phone leashes for all my fishing gear and a neck lanyard for my camera. However, a key float could be very useful for your camera if you don't have a neck or other leash on it. But--be certain to test the camera float in a bucket of water or pool to be certain it will support the camera weight.
We happen to have zero surf along the Forgotten Coast of the Gulf of Mexico, but if I was doing surf launches and returns on a regular basis along the Atlantic or Pacific Coasts, it might be a different story.