There was recently a discussion on the dev mailing list.

This discussion was linked to: https://docs.google.com/document/d/1X6Hap9Hi5qJ9a-XVXmLILol2cBcpXExutw6-adPLAb0/edit?usp=sharing

Historically, it comes up quite often: https://www.google.com/search?q=async+payments+site%3Alists.linuxfoundation.org