Did come across this developer documentation regarding recurring payments:

NVP/SOAP:
https://developer.paypal.com/docs/cl...file-curl-etc/

REST API:
https://developer.paypal.com/docs/in...-billing-plan/

Looked at a version of the osc paypal recurring payments from a general overview perspective. The documentation eluded to difficulty of combining a purchase of something periodic with something one-time (ie non-subscription type product), but thinking outside the box if necessary one could generate a "scheduled" payment of a one-time charge for all of the non-subscription product and a periodic payment lasting the desired duration for the other part.

If anything I would say that one aspect of trying to keep up with such a revision to support this is that it seems that over the years things have changed a lot which means that one (many?) would have to keep up with those changes in addition to the current base/core PayPal operation.