Nicknames placeholder for checking availability; Offline players! (true/false)

[Feldmarschall]

As the title says, it would be great to add a placeholder so that you can check whether the nickname is taken or not. Should also work for offline players.
This allows you to write external commands that are linked to other functions.

For example, an item that is consumed when the nickname is assigned. Otherwise it is like this: The item is consumed and then you are told that the name is taken.