The main forum menu displays the main category as a submenu, so it's obvious that the button label is one of the choices - you can click on either one. If you make the OM button consistent with the forum menu, you'd have two items in the submenu, the new wiki, and the old docs. I think that would be clearer, especially to new users.
It's useful to bear in mind that anything's obvious if you already know how it works.