I guess at this point it is safe to say that whenever you see "rewrite in Rust", it simply means there is no one to maintain the software anymore. They are saying this pretty openly that they weren't able to patch xfwm4.
I only fear that this is manifestation of a wider phenomenon when new software developers are unable to maintain software created by old software developers. If that is so, they will try to simplify the software to what they can actually maintain and rewrite it into a form in which they can maintain it.
If i assume this is true, then all of this is annoying, but actually makes sense: Wayland is simpler than X11, so people will tend to maintain Wayland-related software rather than X11-related. Rust won't let unskilled coders to make some mistakes, so from their point of view it is going to be simpler to rewrite something in Rust.
Although, goodbye network-transparency, goodbye performance, goodbye stability. Oh well, but it's that time of the year.