I don't see much point in it.
It would restrict the privacy without a good reason; what if you move to another country? Would you have to notify the administration (one month before, in two copies)? What if you feel incomfortable to reveal your email address if you wish to register on a random server?
To protect your account, use a good password. If you forgot it, contact a head admin for assistance. So, -1.
A good idea would be automatical blacklisting the nicknames similar (like, with the capital 'i' instead of 'L' or without/with a clantag) to the current one along with the previously used nicknames to prevent the confusion. If anyone tries to connect under such nickname, he would be gently told to change it on join (maybe directly ingame using a dialog box?). So, for Nikola[NO] 'Nikola', 'Nikola[<anything but NO>]', '[<anything>]Nikola[<anything>]', '[<anything>]Nikola' and the same combinations with 'Nikoia' would be blacklisted. What do you think?