This might increase the number of buyers who return to the site, since I'm willing to bet many won't keep checking back every day or week for new articles in their category, and some might not be willing to put up a request. When they get an alert, they might go, "Oh, hey, cool," and check out the site again, maybe even purchase that article and others.
The other thing that could be incorporated is authors being able to view the most commonly subscribed-to keywords or categories. It would help both us and the buyers, without the hassle of setting up a request. (They might not know exactly what they're looking for, might not have an idea about their budget, etc.)
Just a thought.
