Leftover is meant in the sense of being there for backward compatibility. As for the Wikipedia page, it is to give some dates showing when Microsoft added Unicode. But you seem to have a problem believing that UTF8 is possible as the codepage of the locale in recent Windows versions. I am sure you can try it for yourself.
Well, I only see a lot of east asian there. I do see a beta utf8 option though, if I search for it.
Why would it need to be configured out of the box?
As hard it is to explain hacks like the lazarus utf8 hack to
developers, God forbid I have to explain settings about encoding to
end-users.
So it is fine if you can do this on startup of your app, in your app's bubble. If you have to do it globally, it is IMHO useless. Or at least when all of windows supports this (still beta) option.
It is about Unicode, not about UTF8 vs UTF16. I am totally aware of your position on which encoding your want. I personally prefer to see, while I know it will not happen, support for UTF32.
You must write a lot of text renderers (afaik the only thing UTF32 is actively used for )
It's about the normal situation on Windows. And windows is roughly equal to the supported versions (+ say a year of grace period, as we have observed in the past for w2000, XP and vista). So since w8 is good till 2023, you can't make it an requirement till 2024.