Perhaps you could do the following:
The forum starts out as you described. Except that the very rules that it operates on can be modified - like an open source forum which can be modified on the fly. Initially there are a number of rules set up about how the system can be modified: say, a modification in proposed. A poll opens for a week. When the poll closes, if it got higher than 50% approval, the change goes ahead. The rules describing the modification process are of course, also candidates for modification.
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