None of those need improving.Phones are already thin enough,fast enough and have more pixels than an eye can see.Have we reached a peak, I'm know operating systems have, Microsoft for example say they won't release another full OS again, rather updates to existing OS's. So what next for mobile devices. Thinner, faster, higher resolution?
+1combining phones and tablets into one with foldable or rollable screens.
Battery technology improvement
I personally dislike the fact everything's getting thinner and lighter - give me a brick with a kick-ass CPU instead!
I think we will have real wireless charging (charging devices around house or room) before we get better battery life.