For me, the evolving design language of iOS is a pendulum. Originally, we started out way in faux field [1], then iOS 7 brought us into flatland, and I'm curious if the next few years will reintroduce some sense of, what I think Material Design articulates well, "light, surface, and movement [that] are key to conveying how objects move, interact, and exist in space and in relation to each other."

[1]:

A full-fuax interface isn't needed anymore, but I think iPhone OS—iOS 6 did a great job at introducing a touch driven interface to the masses. Making a button look touchable or having pages that curled with your swipe helped take what we knew in the real world, and tie it to this new, touch-driven interaction model.

Yet, time passed and we all got used to the conventions. Today, you can show someone a slightly-rounded rectangle with text inside, and most folks will know it's a button. Same thing with colored icons; there's a instinct to tap on these types of things now. We've acclimated.

I agree with Trevor and Charlie — moving to flatland was a great reset, but I'd like to see the reintroduction of certain skeuomorphic properties to the current iOS design.