I figured something like…
- Logged in more than 33%-50% of days in past month/quarter
- No posts for past month/quarter
- Are at or near the last response in any topic that has X number of posts
The latter point in particular establishes that the user is interested in the topic, has read and hopefully understands the different perspectives on the thing that interested them, then intervenes when they’re most likely to engage… This way it hopefully doesn’t annoy users into commenting on short, trivial spammy topics which degrades quality and costs resources.
Could even have a boomerang / prodigal son badge for them 