For whatever it's worth, Windows 10 is one of my favorite looking user interfaces, especially with its dark theme. I am not sure why so many mainstream operating systems do not offer viable dark themes.
I actually don't mind the Windows 10 UI as it happens, but if there were the variety of options for Windows that there are for Linux, I'd certainly see if I could find one I liked more.
Same goes for MacOS, iOS, and Android.
In a sense though, this is what I consider to be the strength of the windows UI. With the tight coupling, you can make guarantees on the UI covering all possible configuration options. At the same time, it allows a fixed standard of how to implement configuration. (Some of this comes from windows being monolithic)
The end result is a 'unified' UI where there are user-friendly ways to configure a system. Most notably, it is a lot easier to 'explore' the configuration options of windows as opposed to any linux distro.
I do have to say, $9.99 is a pretty good price for this. But this again reinforces my point: if people really hated the Win10 UI that much, a $10 purchase should be nothing to fix it.
Also, I only looked over the link cursorily, but does this fix the whole Metro interface? That's my big complaint with Win10; when you're on the regular desktop, it isn't much different from Win7. It's when you want to load a new program, or use the Settings, or stuff like that you suddenly find yourself in the purple hell that is the Metro UI. If this Windowblinds program is only letting you skin the desktop stuff and not changing the whole start menu, then it's not really fixing the problem, just making the crappy, clunky Win7 desktop more pleasant to use.
I don't like the Windows desktop that much (I like the start menu and such, I don't like the look and feel and other things, which is why I'm a KDE fan). But I can deal with it fine; it's the Metro stuff that's really horrible to me.
1) It's not just MS pushing the flat-UI trend. Apple and Google are too, along with every other Web/UI designer out there. Everyone's doing it. MS's version does seem to be the ugliest though, mainly because of the horrible color picks.
2) The users you seem concerned about like this stuff. They're all buying and using Windows, along with Macs, iOS, Android, etc. devices. There's simply no serious effort being put into any UI alternatives. There's some stuff going on in Linux-land that has a minuscule marketshare, but that's about it; even there, the most popular desktop is Gnome3, which is on the same bandwagon in many ways.