I have a project coming up and would like to use Backdrop.
I'll need a solution for a simple monthly recurring billing system. Right now I'm leaning towards a Paypal subscription button unless there's a better choice in the Backdrop ecosystem.
All thoughts welcome.
RE: PCI compliance, I have a project using Ubercart in development and I expect I'll be porting Ubercart Stripe as part of it. From the project page: