Yeah, there are some other metrics noted in [this Trello card](https://trello.com/c/TezAGRL7/151-notifications-system-health-api-endpoint) that will eventually end up in such an endpoint.

As for this particular metric, my reasoning is that there is something wrong the system if `@expired_oauth_tokens` increases with any regularity. Once the two new workers are deployed, OAuth tokens should only expire due to extended system failures (PG or OC-ID or Redis goes down and doesn't recover quickly)