Absolutely not. Fish may be written in more of a cross-platform language/ecosystem now but as a unix shell, we make heavy use of unixisms that have no windows equivalent throughout its architecture, design, and implementation.
Is it theoretically, someday possible? Sure. Does rust bring us closer? Maybe a tiny bit, but honestly not much (it has a more elegant per-platform targeting/conditional compilation model but it’s nothing that wasn’t possible in C/C++, and we don’t use the “native” oob cross-platform std lib stuff like launching procs).
Looks like rust is reasonably well working with cygwin/msys2 based on some github issues, https://github.com/rust-lang/rust/issues/79854 . Given that, I'd expect that this rust rewrite should work under them at least. Though it's obviously not a fully native build since you've got a bunch of compatibility layers involved to bring in those mentioned unixisms.
Ironically the RIIR project makes this more difficult; we lost support for Cygwin altogether and I think the msys2 stuff would need to be re-explored if it even remains possible.
