Here's the code from our forum. It appears to be implemented, but that PHP is too dense for me to parse:
array(
'tag' => 'quote',
'parameters' => array(
'author' => array('match' => '([^<>]{1,192}?)'),
'link' => array('match' => '(?:board=\d+;)?((?:topic|threadid)=[\dmsg#\./]{1,40}(?:;start=[\dmsg#\./]{1,40})?|action=profile;u=\d+)'),
'date' => array('match' => '(\d+)', 'validate' => 'timeformat'),
),
'before' => '<div class="quoteheader"><a href="' . $scripturl . '?{link}">' . $txt['smf239'] . ': {author} ' . $txt[176] . ' {date}</a></div><div class="quote">',
'after' => '</div>',
'block_level' => true,
),
This is the only occurrence of "link" in the quote tag. It's possible that it's only implemented if you quote another person's post.