This use case is unchanged.

If you specify -target x86_64-windows-gnu -lc then some libc functions are provided by Zig, some are provided by vendored mingw-w64 C files, and you don't need mingw-w64 installed separately; Zig provides everything.

You can still pass --libc libc.txt to link against an externally provided libc, such as a separate mingw-w64 installation you have lying around, or even your own libc installation if you want to mess around with that.

Both situations unchanged.

That's cool. I imagine I could also maintain a MinGW package that can be downloaded through the Zig package manager and statically linked without involving the zig libc? (Such that the user doesn't need to install anything but zig)

That's a good way to sell moving over to the zig build system, and eventually zig the language itself in some real-world scenarios imo.

do you suspect it will be possible to implement printf??

while we're talking about printf, can i incept in you the idea of making an io.printf function that does print-then-flush?