dired-x have no menu bindings.
I think some of the commands fit naturally into the dired menus.
I suggest to bind the commands

   dired-do-find-marked-files
   dired-do-relsymlink
   dired-flag-extension
   dired-mark-extension
   dired-mark-omitted
   dired-do-relsymlink-regexp
   dired-omit-mode

as shown in the first attacment.
The second attachment is a patch to dired-x.el that does it.

Any objections/additions/comments?