The ability to pull in MailChimp and ConstantContact reporting would be a great additional report that we could provide to our customers (similar to how we can pull in Google Analytics). It would give us an even more well rounded look at our client's marketing.

https://developer.mailchimp.com/documentation/mailchimp/reference/reports/

https://developer.constantcontact.com/docs/developer-guides/overview-of-api-endpoints.html