I suggest two levels of classifiers.
"classifier-authoritative" and "classifier-proposer". An authoritative
classifier is the same as the current classifier status. A proposer is
also the same with the addition that classifications made by them are
marked as "suggestions" so the authoritatives can review them at a
later time. (The client might or might not handle suggestive
classifications differnetly from authoritative ones.)
A possible setup could be to make every user a proposer by default.
Of course all this probably needs changing the server some... :)