A rolling download count is what I was thinking about.
I am also having second thoughts about the rising feature. I was thinking about giving new addons a chance to shine, but they wouldn't get a rising indicator with their usual download counts. Maybe you could just make it so that the list can be filtered for addons that have been added in the last 30 days?
The ulterior motive is to get users to try out new stuff. In the long run it would also help if we could mark an addon as an alternative to another addon, so they can check it out when something breaks after a new DLC.