I am using the calendar module. I like how it integrates with Paypal standard.  I realize that integrating it with Paypal Pro may be out of scope, but could you leave a hook in the processs so that I can write my own modules to do it?  What I am saying is when you click on "Enroll", I would like to go off to a different location, confirm payment and then come back into the Calendar module so that my attendees can still be added to the events tables.  What do you think? 

First off this is a great direction; Integrating into a standardized store payment provider. I think it is certainly worth the effort.

There is a good example of this sort of payment abstraction in the ASPDotNetStore implementation. Of course that is a licensed/commercial product however the Store team might glean a gem or two from it.

That being said, I don't feel everyone will want to integrate into a store model or a common provider. So a standard stand-alone PayPal mode would be a requirement for alot of smaller instanciations.

Is there currently open dialog on the direction/timing/effort requirements on an open payment provider model?  Are there any key forum threads that this is being discussed?

Cheers,