I will answer this question basing on what I learned in the period I was site maintainer on drupal.org. My answer doesn't reflect in any way what the current site-maintainers think, or the thought of the maintainers of any module.
The first project queue one would think is the one for the Project module since Drupal.org is effectively using that module, but I think it's improbable the current maintainer would plan to add such feature, if that is not generic enough to be applied to other sites as well. The answer is probably going to be something on the lines of "If you want to implement that feature, you can implement it in a custom module."
Drupal.org does use custom modules to implement those features that are not currently used in any module, or to alter how some of the features are implemented in existing modules.
If the feature request involves writing code, then the project queue for Drupal.org customization project is the best choice. In this case, I would also provide a patch for such feature to be implemented.
If the feature request is about a module to enable, I would use the Drupal.org site-maintainer project queue, since some of the site-maintainers have the permission to enable modules on Drupal.org.
In both the cases, be ready to convince other users this is really necessary. In the case of custom code, it is much preferable to be ready to provide a patch for one of the custom modules used on Drupal.org, if one of the maintainers find the feature request interesting.