[tpearl5]

FYI, until I figure out how this could be integrated into the mod, you can run this query to determine how many threads you would be noindexing if you set it based on words and replies. Just change the 1 after replycount and 15 after words to whatever.
WARNING: this query could take a while if you have a lot of threads. I ran it on one of my sites with almost 200k threads and it took 5 seconds, but results will vary.

SELECT COUNT(*) AS threads FROM(SELECT LENGTH(pagetext) - LENGTH(REPLACE(pagetext, ' ', ''))+1 AS words FROM post LEFT JOIN thread ON (thread.threadid = post.threadid) WHERE post.parentid='0' AND thread.replycount < '1' HAVING words < '15') AS threads;