The backport for the $status operation supports /Subscription/$status but didn't pull back support for Subscription/id/$status: http://build.fhir.org/ig/HL7/fhir-subscription-backport-ig/OperationDefinition-Backport-subscription-status.html

vs R5: http://build.fhir.org/subscription-operation-status.html

We recommend that the single id query is also patched back. This came out of the January Connectathon.