The plugin type is actually called "replicator", to avoid conflicts with the existing source files called "replication.*"
The existing replication system in MySQL 5 is... well. Like the old joke about if you like laws or sausages, you probably shouldn't watch them get made, if you need to think that MySQL 5 replication is rock solid, you probably shouldn't read the source code. Heck, a serious bug was discovered in it at OpenSQLCamp a few weekends ago, just by projecting a random page of code on the wall and having a dozen pairs of eyes read it.