Common Payment System
How about simplifying the life of extension customers and the life of DJ programmers by using a common payment system (API). The sytem below already supports about 20 payment methods (Strip, Authorise.net, ...)
The one I like is here (though Techjoomla also have one)
This will mean DJ write one time to integrate Payage. It will mean extension buyers like us will not have to struggle to find a payment gateway. I need xendit for example. I asked them to interface with Payage. If you were already supporting Payage - then problem solved!