Some controllers or management systems expose NETCONF on northbound interface.
One example is OpenDaylight SDN controller, where NETCONF can be used to change controller configuration. In other words, SDN controller is considered as an end device by the higher-level management system or peer SDN controller.
Another example is Cisco Network Services Orchestrator (NSO), where NETCONF is a primary northbound API. This is what is written in its documentation: “REST may at first sight appear to be simpler to use, but is not as feature-rich as NETCONF… Both NETCONF and REST provides functions for manipulating the configuration (including creating services) and reading operational state from NSO. NETCONF provides more powerful filtering functions than REST.”[1]
NETCONF is a valid interface for managing systems if it is used with vendor-neutral YANG models[2]. It is not only valid for device configuration, but for SDN controllers and other systems management.
[1] NSO documentation about RESTCONF: “RESTful API over HTTP for accessing data defined in YANG. It tries to follow the RESTCONF Internet Draft [draft-ietf-netconf-restconf] but since it predates the creation of RESTCONF, a number of differences exists”
[2] More information about NETCONF/Yang is in phase 1a chapter