Display monthly active users (MAU) in /api/v1/instance
Total number of users isn't a good indicator of site activity. It's common for people to sign up and leave. Large servers are common targets for bots that register accounts and post spam.
In order to really understand the size of an instance, we need a recent statistic. Mastodon addresses this with MAU, which I think is good:
If we can do something similar, it will provide more value than the user count alone.