Subscription products

As a business user I would like to setup subscription products where payment for product will be taken on recurring basis.

Some ideas:
potentially can be something like electronic delivery (e.g. subscription_delivery) which can be in progress as long as recurring payments notifications are received from PG
need to enhance PG interface for recurring payments.
special job for subscriptions to increate the order amount (or add additional line) each time we extend so that payment notifications balance out.

NOTE: this is a YCE feature