We've just done something similar with our product https://fliprss.com - it integrates with MailChimp and Campaign Monitor to solve a niche problem neither solve. We knew it was a problem for at least one company as our client approached us to see if we a product that would allow them to send automated newsletters with multiple RSS feeds based on individual subscribers preferences.

It's since turned there is a demand for this beyond our one client too thankfully.

I think it's helped that this product is aimed at businesses primarily too. With a higher price point we won't need a mass volume of clients to be profitable reducing demand on customer service requests etc.