I really don't think this is necessary. Mene's not all that big and it's not hard to find which threads are really active and which aren't. Usually, if a thread isn't very active, there's a good, or at least decent, reason for it to be inactive. I know I wouldn't want to pay to tell people about a thread of mine when I can just put up a page prize or some kind of game within the thread to attract people which will keep the thread on the first page anyways.