I really wonder what that does. This can't affect the Win32 wide API e.g. GetWindowTextW will still return wide characters (UTF-16 / sometimes UCS-2). Probably this sets the system codepage by default to 65001, so that if you request a string "in codepage format" it will return UTF-8.
It is kind of way too late, but better late than never i suppose.
Qt uses UTF-16, too, AFAIK.
Wow. I think that implies all the ANSI Windows APIs will be able to use UTF-8 as well. Native UTF-8 support is something that Windows developers have wanted for years. I thought it was impossible because of some API limitation where it assumed multibyte characters could only be three bytes long, but maybe this assumption has been removed.
EDIT: So I just tested this. It does seem to affect the ANSI Windows APIs: https://0x0.st/siCS.png
Unfortunately, this doesn't mean the average Win32 program will be able to start using UTF-8 internally, since the ANSI codepage is a system-wide setting, so you won't be able to opt-in to UTF-8 per-process (at least, I don't think this is possible.)