Username serialization - security/privacy update

I know that this would probably need server mods. If usernames were serialized, so that each time a given username expired on the Soulseek server, its next incarnation had its serial changed, then when the client recognizes the changed serial, it can block/alert/message to prevent new users from having access to shares that were granted to other people who had previously used the same nicks? Makes sense? A timestamp or hash would eliminate the need for a database?