The battery life of the phone, the potential longevity and repairability of the phone could be amazing. The last two are why they don't mabe them so much, and there's no demand when there's no product to meet that demand.
Me? I want a phone that floats, out of the box. Bonus points if it can survive a fall into a barge wing-tank, including hitting the ladder on its way down, but really, taking my phone off the boat is a habbit I never got into.