Any communications-auditing regime relies on detecting and preventing steganography. This can be immediate successful, but is an endless escalation that should cause honest people (ie those who aren't trying to restrict communication) to focus on node security.
While an IDS can indeed benefit end users, its same functionality can be implemented as edge software - either on the nodes, or if worried about nodes being already compromised, then a separate "network processor" domain. The only point of needing a centralized IDS is the centralization - top-down control.