I suggest working with Jack Arturo, the author of the incredible WP Fusion plugin. Specifically, the ability to add/remove people from lists based on actions they take on our sites. Right now there is very limited capability with it. Adding people to lists when actions are taken, but that's about it. Removing from lists is vital too because WP Fusion has the ability to restrict content based on the list a subscriber is in. For instance, if I have a membership site with recurring payments, I could have WP Fusion add a member to a MailPoet list when they subscribe. And then later if they decide to cancel recurring payments (membership), WP Fusion can remove them from the list. I'm sure Jack would be glad to work with you on this. https://wpfusion.com/