Earlier quoted context omitted.
Congratulations on almost 6k stars and 0 open issues! That takes a lot of work to keep up with the issues and very good documentation to avoid unnecessary usage issues.
Give me access and I'll get your open issues to 0. ;) But seriously, that's a good idea for a metric.
Yep, isitmaintained.com uses issue resolution time and open percentage of issues/PRs as the metrics: http://isitmaintained.com/project/pubkey/rxdb :)