I think the new UI could work absolutely fine. Only problem is all the GUI elements are so large. It’s like a telly tubby play set.
That is my biggest complaint with windows 10 as far as usability, that and everything is hidden and hard to get to. If you're not on a 4k screen, everything is so big and blocky and takes up so much space too. It's really inefficient UI design. Anytime I want to do something simple I find myself having to hunt around trying to find something that was easier to find in XP and 7. It's not "being scared of change" but rather realizing that some things don't actually need to change because they work.
That, and all the white. Way too much white. It hurts the eyes to use. I feel like I need to wear sunscreen and sun glasses if I'm going to use windows 10 for longer than 5 minutes. To make matters worse other than choosing between like 4 crappy themes that are all one extreme to the other, there is no way to customize anything. Even Windows 3.11 let you customize stuff.
Microsoft have thrown away 20 years of knowledge of GUI when they released Windows 10!
Through the 90s and 2000s MS did the right thing and focused on making their UI consistent. Widgets had a raised effect: push a button, with the mouse and it went from protruding to recessed. Window titles were nice and bold, with a reasonable contrast with the background. This is one of the advantages Windows had over UNIX. Change the colour scheme or skin on MS Windows and everything would change. On UNIX, different programs were often made with different widget toolkits, each with their own settings. The only thing that was consistent were the windows, which were drawn by the same window manager. This has been largely fixed now, for example if you're using KDE, you can set GTK+ to render as Qt, so GTK+ programs look the same as Qt programs.
Now, on MS Windows 8+, all widgets are flat and the whole UI is extremely inconsistent. There are traditional programs, which use one widget toolkit and new Metro apps, which look totally different, with their massive fonts and widgets, optimised for a touchscreen. The whole thing is a total mess!
If you had a 4k screen, then I'd suspect many of the traditional programs would look too small. It's possible to change the size of the UI, but if one set it so the Metro apps look good, the other GUI elements would become too small.
See the attached. Look at how small a traditional program (Character map) is compared to a Metro app (Display Settings).