There’s no report to show subscribe/unsubscribe activity. Please add this, and/or provide a hook so that we can take action on these events. It’s important to know when we lose someone, and what they were reading when they made the decision.
For a hook I think we would just need the user ID, email address (if they’re not a member), and the Newsletter ID which led to the UNsubscribe request. From there we can use a custom function to get a timestamp, log other similar events, establish patterns of subscriptions and cancellations, etc.
I will look at the code as time permits, but it would help if a developer could point to existing hook, and suggest the ideal place to add a do_action for a custom hook for this, until a formal enhancement is added (if ever).