The most interaction with the fallback DNS servers I can see is in dnsperf.info where I can see how the servers are ranked by delay, but I would be really nice to see in the logs somewhere which DNS server is being used to resolve names. I currently use multitail to monitor the logs for changes
Screenshot.
So a solution I imagine would be cool was customizing the log format that gets saved on disk. As far as I know the formatting in the config file only pertains to the live log output on Android. And some way to include stuff like which DNS server is doing the resolving would be really neat.