I would rather see on-going metrics presented in an easy to understand way that a good portion of the community (not just 20k+) could view whenever they got curious instead of a formal check-in or review. Maybe some of the most popular SEDE queries would be a good place to start looking for inspiration. (I’m writing this from a SE perspective, but I think some of it translates to other communities and networks).
I’d like to see some friendly rivalry among sites around keeping metrics in the positive zone. Leaderboards are very motivating for some folks. If the metrics are designed well, I should be able to compare ELL to Stack Overflow. For example, what percentage of the “good” questions asked this fortnight have more than one upvoted answer? If “good” is defined in way that normalizes out activity differences, it shouldn’t matter too much how big a site is in terms of active users and traffic. “What percentage of the active community with access to certain privileges (close votes for example) use them with some amount of frequency?” might be another metric where “active” is measured against the median activity for a site rather than some fixed “visits per week” threshold. (I don’t know if those are good metrics for community health or not; they’re just off the top of my head)
There could be a bunch of metrics with more being added all the time. Maybe metrics get a test run to see how meaningful they are and get decommissioned after a while if they don’t contribute much value. Each individual metric doesn’t have to be a KPI (key performance indicator) to have some value when looking at how different aspects of the community are changing over time.