I would like to see the possibility for a resolver plugin. E.g. for using a different resolver library (and new options) like we did with wget1.x when adding support for c-ares a while ago.
Just FYI, I am currently working on service based IP address lookups using NAPTR and SRV DNS entries, called DNS-SD (if interested: https://tools.ietf.org/html/rfc6763). Not sure if there is anything other then SIP using this mechanism in reality.