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How about having user dashboard where we see activities of users like which user joined which list or unsusbcribed etc etc as otherwise it wil be tough to monitor growth of individual lists
You can already see your subscribers growth via the graph chart in any subscriber list:
You can also see all activities of your subscribers all at once or separated by statuses (eg. unsubscribed, bounced etc) at the bottom. Whenever there is a status change for any user, they will float to the top of the list so you can see it.
Hope this helps.