Update 2017-04-17: since the publication of this post, many things happened:
- the procedure for fixing a crashed slave has been automated (Bug#77496)
- Bug#80103 as been closed at the same time as Bug#77496
- but I still think there are unfixed things, see Bug#81840
I will be talking about parallel replication at FOSDEM in Brussel on January 30th and at Percona Live Santa Clara in April (link to the talk descriptions here and here). Come to one (or both) of those talks to learn more about this subject.