Right now the main disadvantage is that GNOME Shell is single-threaded, and handles not only those JS extensions, but also essential tasks like window compositi

Right now the main disadvantage is that GNOME Shell is single-threaded, and handles not only those JS extensions, but also essential tasks like window compositing. This means that a misbehaving extension can freeze the whole desktop, which is especially bad on Wayland where that includes the mouse cursor and input processing. I still prefer GNOME for the rest of its UX, but if you ask me, the next rewrite can't happen too soon. Edit: I noticed that some of the new improvements seem to be addressing just this, so what I'm saying may be out of date in regards to the latest version.