Woah Garmin...
They really are on fire at the moment. I have the 935 watch for triathlon which really is superb when put next to it's nearest rival which is the Suunto Spartan. The crappy overpriced iWatch doesn't even come close to either of these in terms of sporting pedigree.
Take the 935 then and add a more rugged casing and you get the Fenix. Take the 935 + Fenix and add full dive management and pressure sensors and you have the Descent for scuba diving as well as almost every other conceivable activity you can think of (I did say almost!!)
So it's the Descent that I am now looking at trialling as my new single watch to do everything.