I think this is a fascinating experiment and will be interested to see how this goes. Many people look at Open Source and say "Why would I pay ChargeBee or Recurly $300 or $3000 per month when this is free?" Seems like a no brainer. But when it's running your billing and it's driving $100,000 or $1 million a month in revenue then it's looked at from an entirely different view. Saving $1000 a month is great but if it means you are missing out on $5000 or $10,000 because you can't support a business model then it isn't such a great proposition. Now I'm not saying Kill Bill is better or worse than the alternatives. Just that open source solutions where the effects on productivity and revenue are so clear are judged by a different type of measurement than other areas.

Good luck!