“rewrite (the easy parts of) $battle-tested-ancient-coreutil in rust” seems interesting as an exercise or as a way to learn a new language, but i’m not convinced of it’s broader utility.
I would argue that "the easy parts" of cp account for a very significant fraction of its usage (i.e. copy some files/directories without any other options). The idea with fcp is to make that common use case very fast, not to replace cp and all the options it handles.
I definitely can understand the fatigue with "rewrite it in Rust" though, as there is a lot of that.
Something you might be interested in is that people have actually gone through the effort of rewriting the actual coreutils to spec in Rust (https://github.com/uutils/coreutils).