I think the reason they're trying to make phones thinner each year is because they're working on foldable phones, where ideally you'd want 1.5cm or less once folded. Surface phone and such will be the next big thing in 2019-2020. I can see Note X being like a mini surface pro maybe with screen unfolding into 1 big one.
Like the device they showed off a few years back.
Tablet, not so much, but the phone to tablet concept I like quite a lot.