I was looking for the same thing but for email providers. I would like to let users to subscribe to mailchimp,aweber,getresponse etc using a single integrations instead of having to integrate each one of them.
We have a very simple interface for email here: https://cloudrail.com/unified-email-api/ But it just offers sending emails. What you described is actually a potential candidate for a next interface. Would love to discuss that use case with you. Feel free to reach out: support@cloudrail.com