> (reads local stats from files or proc or whatever)

If there's useful stats from /proc we're missing, we accept PRs.

> about half run on the Prometheus node itself and talk to services like ElasticSearch or Postgres.

That doesn't sound right, those two should run on the ES/Postgres nodes.

Only things like the blackbox exporter and snmp exporter should be considered for running beside Prometheus.

> When I have time, my plan is to write a small HTTP server that spawns plugin as subprocesses that emit their metrics via stdout, which seems like a much more reasonable, low-maintenance solution, and something node_exporter ought to support in the first place.

We went with the textfile collector approach, rather than reinventing cron.