The only thing that would be on my wishlist that isn't here now is publishing metrics via statsd. Timers for successful and failed requests to iprepd, counters for accepted and rejected connections, and maybe a set for the ip addresses seen would all be useful.
From https://github.com/mozilla-services/iprepd-nginx/pull/1#pullrequestreview-169359004
Could try out https://github.com/lonelyplanet/openresty-statsd/blob/master/lib/statsd.lua or write our own.