A small observation: the policy of restricting ! rewards based on the number of ! rewards in the post is not "centralized" control. This rule is based on the information that is in a given comment. The rule is not based on a centralized database.

Accounts sharing a blacklist is a form of centralized control.

Of course most of the tribes on HE use the same mechanism (scotbot) to distribute the rewards. So, it is actually impossible to avoid some centralized control.