Note that another FEP Process improvement related issue was started by @nutomic.
Cross-referencing to:
A possible solution boils down to Compliance Profiles once more, where:
Good implementations tell you what FEP’s and other extensions they support.
(PS. I just checked if the XEP has something like this, and then found Service Discovery to be similar to Compliance Profiles and able to deliver fine-grained Features to discover.)