If scale is a function of read/writes, very large. In fact with relatively minimal (virtual) hardware it's not insane to see a cluster doing around 1M writes/second.
Truthfully at Wavefront we've taken the json status directly into telegraf. Plus a bunch of python tooling to massage additional telemetry on a clusters health (coordinator reachability for example).
Plus even more tooling (mostly Ansible) for managing large fleets.