Voting starts in March for the Drupal Association Board election.
Currently wysiwyg_get_css() assumes the CSS is local, but that's not necessarily the case in D7, where drupal_add_css() can take external CSS. The attached patch makes external CSS work, loading in the editor iframe when "Use theme CSS" is selected. Tested in TinyMCE.
It would be nice to have some way to do external CSS in D6 WYSIWYG, where drupal_add_css() isn't an option, but I'm not sure how that would work.