Galaxy S5 was waterproof with a removable back. All the current waterproof phones have SIM card trays, mic holes, cord connectors, speakers, etc, so it might not be as 'extreme' as you're thinking. Just need a continuous rubber gasket and a tight fit. Of course making your phone out of materials that bend or shatter instead of flexing becomes a bigger problem, especially since the former offers no practical benefit beyond 'feel'.