I was thinking of this more for the actual follower count, because Nostr has such a low retention rate.

🌐 stats.nostr.band
I always assume that a good percentage of people who follow me have either dropped off, or lost their keys. I know of a handful who have moved to new keys for sure, but their old account remains as well. It would be nice to have a way to limit the counting of people who haven't had any activity in a recent timeframe.
Followers active in the last week.
Followers active in the last month.
Etc.