This looks amazing. Looking at relay makes me think that the reason Facebook only released a boilerplate implementation of flux was to start spreading the ideas; relay seems like flux++ in that it is an advanced implementation without any of the cruft (like the verbose dispatcher and action name constants).
I'm interested to see what the server-side components of Relay will look like, especially with the pub-sub/server push functionality mentioned at the end of the presentation. Hopefully that will be included in the reference implementation being released.