If I change my nickname from Dude! to something else it is possible for some other member to use that nickname. Sometimes it might be convenient to change a nickname to a new or previously used name. To prevent any abuse however, I think it would be a good idea if there was a nickname history for every member that would prevent other members from using another member's previous nickname. If necessary there could be restictions that would allow a user to only select a certain number of previous names, or to exclude names that do not have sufficient history or number of posts.
Even if there is currently no support or restrictions enforced by the software, perhaps Oracle could at least come up with a policy that provides information and guidelines to assist users or provide the background for arguing on a per case basis to protect people's interest. For example, such a policy could reserve the right of members to use a previously existing nickname, or deny the use of a nickname that is too similar to another, when requested.
There is a related discussion: