Uncluttered and ornament-free is functional but it is also a bit boring. Maybe we can make UI feel a little rougher without losing usability.
If I had to hazard a guess I would think that UI will become more kinetic. We already see this with things like the bounce at the end of a scroll on OSX and phones, as well as with window animations, but it can probably be taken further. The interface could become more like a living, breathing thing than just a piece of paper with some rectangles on it.
Think of a cat: they all have the same basic pieces, they have fairly consistent behavior traits, but they all have different fur and eye colors. The computer could become something of a useful pet.
But that's just my pie-in-the-sky vision, predicting the future is a mug's game.
Movement cues and allowing more 'harmless' interactivity in interfaces is a great way to make them more clear while keeping their static visual appearance ultra-minimalist.
I think UI design is one of those case where competition does not foster growth. Companies feel insecure and try to out-fashion their rivals with stylish designs, forgetting the true purpose of interfaces through passionate and radical opinions that make great blog posts but really don't translate well to such a concrete and down-to-earth trade.
Oh, it's already happened.[1] I couldn't actually find one with christmas lights but I'm sure one existed at some point. Ten years ago there were millions like this. Some of the wildest stuff came out of Japan where there was a plugin that let you completely rearrange the layout of the windows. (They were tricky to find back then, pretty much impossible now.)
Developers pushed back against rampant customization a few years ago when they got tired of people complaining about problems caused by buggy skins. But some apps such as Firefox[2] still have limited themability that could one day make the fad start up again.
[1] http://winampheritage.com/skin/unison-brainstormed-v5/146159
Less is a bore?
If I want an experience, I'd rather go bungy jumping or parachute diving or whatever. When I want to get on with some work, I want to just that; not participate in a shallow, "user experience", desperate to justify its existence to itself.
[...]
"Such a disappearance is a fundamental consequence not of technology, but of human psychology. Whenever people learn something sufficiently well, they cease to be aware of it. When you look at a street sign, for example, you absorb its information without consciously performing the act of reading.. Computer scientist, economist, and Nobelist Herb Simon calls this phenomenon "compiling"; philosopher Michael Polanyi calls it the "tacit dimension"; psychologist TK Gibson calls it "visual invariants"; philosophers Georg Gadamer and Martin Heidegger call it "the horizon" and the "ready-to-hand", John Seely Brown at PARC calls it the "periphery". All say, in essence, that only when things disappear in this way are we freed to use them without thinking and so to focus beyond them on new goals."
-Mark Weiser, The Computer for the 21st Century: https://web.archive.org/web/20141022035044/http://www.ubiq.c...
"A good tool is an invisible tool. By invisible, I mean that the tool does not intrude on your consciousness; you focus on the task, not the tool. Eyeglasses are a good tool -- you look at the world, not the eyeglasses. The blind man tapping the cane feels the street, not the cane. Of course, tools are not invisible in themselves, but as part of a context of use. With enough practice we can make many apparently difficult things disappear: my fingers know vi editing commands that my conscious mind has long forgotten. But good tools enhance invisibility."
-Mark Weiser, The World is not a Desktop, ACM Interactions: https://web.archive.org/web/20141109145219/http://www.ubiq.c...
https://upload.wikimedia.org/wikipedia/en/8/81/Nato.0%2B55%2...
And to me it makes sense. It's not that different to me from say a pictographical vs a phonemical representation of human language. They can both do the job very well, you usually pick one or the other and stay with it. Altho, arguably the phonemic representation is more flexible than the pictographical alternative --and we see that with pinyin and romaji serving a purpose in pictographical writing systems.
So with interface symbols, once you learn the cues, it's just as useful as the "full color" version