At least they are honest regarding the reasons, not a wall of text to justify what bails down to "because I like it".
Naturally these kinds of having a language island create some attrition regarding build tooling, integration with existing ecosystem and who is able to contribute to what.
So lets see how it evolves, even with my C bashing, I was a much happier XFCE user than with GNOME and GJS all over the place.
You know that all the Wayland primitives, event handling and drawing in gnome-shell are handled in C/native code through Mutter, right ? The JavaScript in gnome-shell is the cherry on top for scripting, similar to C#/Lua (or any GCed language) in game engines, elisp in Emacs, event JS in QtQuick/QML.
It is not the performance bottleneck people seem to believe.