Interesting - but will the extra weight/drag and its effects on the C of G both longitudinally and vertically on the aircraft be acceptable.
I think you would have to vastly increase the thickness of the engine bay doors to provide sufficient buoyancy to stop the aircraft rolling over.
The area around the engines is subject to high temperatures which will have to be taken into account - also if the blades make water contact at significant RPM during the ditching, they will probably tear the transmission and possibly the engines off anyway.
If someone makes it law it will happen - if not then don't hold your breath (no I mean do hold your breath cos you'll be upside down)