It looks like your service is a front-end for existing payment processors, some of whom already offer recurring billing products. How do you differentiate your service against something like Braintree's Vault and recurring billing?
Certain functionalities like Dunning management (follow-ups for card failures), proration logic, readily available custom hosted pages, coupon code support, metered billing etc., In all we have tried to build ChargeBee as an extension of your app specializing in subscription business needs.
We will start providing extensive reports, integration to accounting, CRM systems to help manage entire accounts receivables function. Hope that helps.