Well we can consider that pgloader already implements the first half of the streaming replication: the base copy to stream changes onto.
Adding support for the MySQL binlog replication format is on the TODO list, if you're proficient in it I would welcome hints to implement it correctly.
In terms of priority and organisation, it's Open Source so you know how it works right? Contributions are welcome, as are feature based sponsoring.
This would be the best way to do a migration without braking an existing system.