We’ve published an initial draft of the requirements document for the RPC layer on the project’s GitHub wiki: https://github.com/apple/foundationdb/wiki/FoundationDB-RPC-Layer-Requirements. The intent of this layer is to provide a straightforward and stable protocol for clients that makes it easier to write pure language bindings (i.e. not dependent on our client library) and simplifies the story around versioning and upgrades.
If this is a topic that interests you, please take a look and let us know what you think! Feel free to provide any feedback directly in this forum thread or a new one, as appropriate.