Use the Global: View area to reference another display of the same view

It looks like the code to detect recursion already exists in the render function so here is a patch that allows you to select a display of the same view.

I'm not sure what you mean, but if you can explain a bit further I might be able to learn a thing or two and roll a patch... otherwise the ball's in your court.

It looks to me like that is already done...

<?php
class views_handler_area_view extends views_handler_area {
  // .....
  function render($empty = FALSE) {
  // ....
      // Avoid recursion
      $view->parent_views += $this->view->parent_views;
      $view->parent_views[] = "$view_name:$view_display";

      // Check if the view is part of the parent views of this view
      $search = "$view_name:$view_display";
      if (in_array($search, $this->view->parent_views)) {
        drupal_set_message(t("Recursion detected in view @view display @display.", array('@view' => $view_name, '@display' => $view_display)), 'error');
      }
      // ...
  }
}
?>

This is now broken due to #1215602: views_get_views_as_options() for simple use in #options.

See http://drupal.org/node/1215602#comment-5195532

New patch. Setting to major because it can break existing views if sites are upgraded.

If you read the previous comments from when this was initially committed it was agreed that recursion prevention already exists and therefore it is not entirely necessary to prevent users from trying to reference the same display. So essentially views_get_views_as_options has to be fixed only to improve the usability of embedded views in views areas. #1215602: views_get_views_as_options() for simple use in #options has introduced a regression and the fix for it is being blocked on a minor usability issue? I think this patch should be committed to fix the regression and then we can create a new issue to remove the option to embed the same display.

you can now embed the same display of a view to a view

Well you can add it, but views_handler_area_view::render() will prevent it from executing. It would be an edge case as no one who was thinking straight would try to do this.

Is it so hard to fix another part of the code?

I guess not, I could say the same thing. I'm not on my development machine at the moment so I've got no Drupal install to test it on. Might take a look some other time.