...
See section 6 of the R&S Entity Category specification for a precise definition of the minimal subset of the R&S attribute bundle.
If an IdP restricts attribute release to some subset of R&S SPs, can that IdP declare support for R&S?
The short answer is no. An IdP must release attributes to all R&S SPs before it can assert the REFEDS R&S entity attribute in metadata.
Consider, for example, an IdP that releases the minimal subset of the R&S attribute bundle to any SP that is a member of both the Code of Conduct category and the Research & Scholarship category. That IdP is not eligible to receive the REFEDS R&S entity attribute in its metadata.
As another example, consider an IdP that releases the minimal subset of the R&S attribute bundle to any R&S SP in the InCommon Federation (but no other federation). That IdP may not receive the REFEDS R&S entity attribute in its metadata.
Finally, consider the following counterexample. Suppose an IdP releases the minimal subset of the R&S attribute bundle to any R&S SP provided the user is a non-student. That IdP may indeed receive the REFEDS R&S entity attribute in its metadata since it supports the R&S category "for some subset of the Identity Provider's user population," as required by the REFEDS R&S specification.
Are Service Providers allowed to request other attributes?
...