The kids on my server change names so often it is hard to keep track of. It would be helpful to have a way to translate nick and ign.
Currently I can use /realname to find the ign of a nickname if player is online or /whois to show the nick of an ign if they are online. It would be great to have these translate names while player is offline.

Not really sure that this feature is all too necessary -- nicknames are only relevant when players are online, and if you aren't sure who logged off with a particular nickname you can just check your server console.

In addition, since searching for a particular nickname would probably require reading all userdata files, which would be slow.

Will keep the "open to PR" tag in case someone knows / finds a sane way to implement this, and wishes to do so, but I don't think it'll happen.