In that long-a$$ New Yorker
profile of Jony Ive from back in Feb., there's a (somewhat amusing) reference to the "new display technology" (i.e., good old AMOLED) used in the watch:
He went on to explain that an Apple Watch uses a new display technology whose blacks are blacker than those in an iPhone’s L.E.D. display. This makes it easier to mask the point where, beneath a glass surface, a display ends and its frame begins. An Apple Watch jellyfish swims in deep space, and becomes, Ive said, as much an attribute of the watch as an image. On a current iPhone screen, a jellyfish would be pinned against dark gray, and framed in black, and, Ive said, have “much less magic.”
Sounds like Ive is enamored enough with AMOLED that it may indeed make its way to the iPhone (plus, isn't it required for "Force Touch")?