Support for storing the MySQL privilege tables in a transactional engine was added in MySQL Server 5.6. This allowed the MySQL Servers in a MySQL Cluster to share the same privilegess by altering the privilege tables to NDB. Next step is to allow replication of the privilege tables to a slave cluster. Since the binlog for replication may be written by any MySQL Server connected to the same cluster it's necessary to distribute the queries used to manipulate the privilege tables to all MySQL Servers in the cluster. How to perform the distribution is already implemented in MySQL Cluster but a hook is neccessary to make it possible for a handlerton to plugin and detect when a query modifying the privilege tables occurs. The feature is already implemented and released in MySQL Cluster 7.2(based on 5.5) as well as in upcoming MySQL Cluster 7.3(based on 5.6). It was originally scheduled for MySQL Server 5.6 as part of WL#6004(which described _both_ storing the privilege tables in a transactional storage engine as well as the hook for distributing the statements modifying privilege tables). But since semantics was unclear, it was dropped from there and decision was to write a new WL describing the semantics.