Hi Evan!
It is a complete reimplementation of the remoting layer which is based on actors, and totally lockless. It also features a new Transport SPI that enables people to implement different drivers, so they can use whatever protocol/technology they want, not just the bundled ones. It is now also possible to use different transports at the same time to talk to different actor systems, although this particular feature might be removed if we find it braking some of the underlying assumptions.
I am pretty sure that there will be a nice blog post on
letitcrash.com about the details :)
-Endre