I think they should be use the account_payment module as all the current states will be enought to know the state of the remote payment. The other fact is in ecommerce normally each payment is payed separately so I doubt if it has sense to group them.
I’m wondering if anyone wil require to create the payment before the invoice if it’s created. In this case, the payment should be created without any oriign, and then linked receivable line to know it have been payed.