I imagine "semi-done" means "works enough that it can be dogfooded by the devs and tried out by the curious among us, but does not exactly mirror behaviour of GNU cp in terms of corner cases and error output".

I think we need to be more flexible than classifying things as done/not-done. Even GNU coreutils has open issues[0] - is it "done" or "not done"?

[0] = https://debbugs.gnu.org/cgi/pkgreport.cgi?pkg=coreutils