Restarting Gnome Shell 3.28.1 on Fedora 28

In an Xorg session one can restart GNOME shell without losing application state as applications are running against a separate server (X). But unlike Xorg in case of a Wayland session GNOME shell is not separate from the Wayland protocol, GNOME itself acts as the display server.

So there isn't any way to restart GNOME shell in Wayland without losing application state as the display server also goes down. It's similar to restarting X server in an Xorg session.

That is the reason why this shell restart option is disabled in Wayland (recall that usually the key sequence to kill the X server is also disabled by default in the Xorg session) and there will probably never be any non-destructive way to restart GNOME shell in Wayland.