Comment 1 for bug 669744

I believe this is intentional. You don't need mysql protocol plugin to migrate stuff as there is the drizzle protocol plugin. All the mysql protocol plugin does is make drizzle listen on port 3306, so the conflict would be intentional as there would be a port conflict out-of-the-box. Port 4427 still understands the MySQL protocol and all drizzle clients now use that.

What I am basically saying is you probably don't need drizzle-plugin-mysql-protocol.

I will assign to mtaylor anyway to confirm what I said above.