We can create on drop in replacement which would be extensible through plugins/hooks
Looking to make subscription management platform with plugins for multiple payment gateways, tax/vat compliance, fraud checking, invoice, automated, failover, emails etc...
Reports for revenue, churn rate etc...
Anyone interested?
Killbill is one which has majority of the things you need it seems project contributers aren't willling to maintain plugins and it seems difficult to setup.
But they all feel either short of features, or not extensible or not self hosted.
So, this time i really want to put together efforts and build something on github so that everyone can use it in their SaaS project.
First, regarding maintaining plugins in general, the project is over 7 years old now. We have everything from very small to very big companies using us (some of them have their logo displayed at http://killbill.io/), each with their own requirements. Over the years, we have created about 60 plugins to fulfill these, and the matrix to maintain has become huge (company X is using feature F of vendor/plugin Y with Kill Bill version Z).
It's getting impossible for us (core developers) to maintain all of these for each combination of {F,Y,Z}, while also continuing to maintain and improve the core codebase. This is why we are asking more and more for the community to help us (read: submit PR) and we are more than willing to provide support and guidance (if you want to fix something specific, feel free to reach out on the mailing-list).
I also agree that Kill Bill can be difficult to grasp initially. We've been working hard over the past year to improve our manuals (http://docs.killbill.io/) and API docs (https://killbill.github.io/slate/). There is always more we could do, so happy to iterate if you have specific feedback. That being said, subscription billing and payment is really hard, and after reviewing requirements for dozens of companies over the years, none are alike, hence the complexity of Kill Bill (it's a generic system with lots of knobs to tweak to fulfill most requirements).