Launching sushi does not work under Wayland because the nautilus code does unchecked gdk_x11 calls here:

void
nautilus_files_view_preview_files (NautilusFilesView *view,
                                   GList             *files,
                                   GArray            *locations)
{
        gchar *uri;
        guint xid;
        GtkWidget *toplevel;

        uri = nautilus_file_get_uri (files->data);
        toplevel = gtk_widget_get_toplevel (GTK_WIDGET (view));

        xid = gdk_x11_window_get_xid (gtk_widget_get_window (toplevel));
        nautilus_previewer_call_show_file (uri, xid, TRUE);

        g_free (uri);
}


this needs a runtime (and compile time) check for X, and just pass 0 otherwise.
Of course, sushi needs to be able to handle 0, too.