This is using Netty Executor (NIOLoop) to process AMQP.
Instead of using a lock to enter the AMQP processing, what has issues on scaling up multiple connections per queue, it's using a single threaded executor.
This represents a major improvement in AMQP. I will take my time to write a blog post about this with multiple scenarios comparing 2.6.3, master (before this change) and after. (I will post a link here to this JIRA).