You proposal was added to the wish, but we are currently not implementing any user wishes. Priority is joomlacomment 4.0 joomla 1.5 native.
However I have a quick and dirty solution for you.
go to plugins/content/joscomment.php
goto the funciton pluginJosComment.
function pluginJosComment($published, &$row, &$params, $page = 0)
{
if (!$published) return true;
global $option;
require(JPATH_SITE."/administrator/components/com_comment/plugin/com_content/josc_com_content.php");
}
function pluginJosComment($published, &$row, &$params, $page = 0)
{
if (!$published) return true;
$usertype = JFactory::getUser()->usertype;
if($usertype) {
global $option;
require(JPATH_SITE."/administrator/components/com_comment/plugin/com_content/josc_com_content.php");
}
}
This will hide the comments from unregistered users and nobody will even know that there is a comment software until the user log in.
Nicer solution would be to show a text - log in to see comments, but this demands bigger code changes.