This looks good to me. One suggestion: perhaps the list of previously rejected names could be kept to provide instant filtering to future potential applicants, thereby reducing the burden on the chosen ones. Similary with your retirement option, it seems to me that those account names should be retired also, to prevent future confusion. I hope and expect that retirement will not be so prevalent as to cause any significant inconvenience among new users.

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I'd like to be able to assign to an luser