We are working on prioritizing and filling user requests. We would love to get a better feel for which services have the highest demand for easy integration with Formidable. We have added Zapier integration, and removed all requests that can now be done through them.
Update 4/26/2016: Stripe integration is now available!
Update 1/10/2016: A WooCommerce integration has been released. A third-party has developed another version as well with all the features you would want for creating products from the front-end.