This proposal from the FIX Orchestra Subgroup provides the details of the FIX Orchestra Technical Standard Release Candidate 4.

FIX Orchestra was conceived as machine readable rules of engagement between counterparties. As such, it is a standard for exchange of metadata about the behavior of FIX applications. Orchestra is intended to cut time to on-board counterparties and improve accuracy of implementations.
FIX Orchestra does not change FIX protocol itself in any way, nor does it make obsolete existing FIX engines or tools.

The fourth release candidate documents for FIX Orchestra can be found here:

The main theme of Release Candidate 4 is to refine the Orchestra XML schema to optimize tools.

The proposal is following the technical standards review process described in the document found here:

This release candidate now enters a public comment period in which public review and feedback is encouraged. The public comment period will run for a period of 90 days beginning on the 25th of February 2019.

Please post feedback, comments, and questions as replies to this discussion thread.