Believe me, we know that people are interested in more icons! The problem is, icons are one of the most expensive things that a site can offer -- it's not even the cost of storing them and transfering them that's the problem, although that can be an issue sometimes, but the issue is that the more icons someone has, the less likely that a particular icon will be in the memory caching system we use to speed up the site and avoid overloading the database. We also have to be very careful about how we offer add-ons, because our paid account prices were set very carefully to make sure that we would be able to continue to keep the site functional based on some predictions we made about future usage -- because we're 100% user-supported and accept no outside investment, venture capital, or advertising, we have to be very careful with anything that could affect the paid account percentages and usage we designed for.

We are planning on making the ability for people to buy extra icon add-on packages to add to their paid account, but we're very, very unlikely to ever add the ability for people to buy icons only without a corresponding paid account. Way back when Dreamwidth was still in development, I wrote a long explanation about why this isn't practical for us: you can read those here and here. Still, Mark's planning on working on the extra icon add-ons starting in early January, although the payment and account capability system is very very complex and it might not be an immediate thing!