for strfry specifically, it can "log" the performance metrics but this does not easily equate to being able to measure them from external systems unless you were to ingest the logs and turn them into metrics.  That being said, you could ingest process metrics, disk metrics etc, and use this.  Right now the focus is to use the data currently accessible via the interceptor-proxy such as #REQs/second, #subscriptions and #events, use that to surface the information about how much a particular login/pubkey is 'using' vs other usages, display that to the relay operator so they can make a decision about allowing or blocking.  once this is done, then i can think about cost tiers or etc..