Seems a good solution and would mean you could change your watch whilst still retaining the smart element.
My concerns with this would be two fold, firstly, the paltry WR would mean removing that part of the watch when you swim which leads onto the second concern; when fitted, it will make the watch head thicker. If you wear your timepiece on a metal bracelet I imagine this will need readjusting.
Good idea in concept. If something could be made into a buckle that might work. Either that or a decent watch with a Breitling Cockpit module style part of the bracelet.