One of the things I've been rolling around in my mind for a while now is what would a "what's old is new again" reversion to the non-flat/minimalist style look like if done now.

One of the things that strikes me with 4k displays is that there's a lot more pixels to throw around at elaborate designs, along with the skeuomorphic/physical representation of interactivity. I'm thinking back to the winxp era uxstyles skins that while they demonstrated Sturgeon's law, also had a wide range of art and ways to make it approachable for people.

In the case of windows, changing UI approach again would add another layer of strata with inconsistency, but right now MS's approach comes across as resume led design with a new version of windows to launch with their stamp on it