I really hope NuclearJS (by optimizely) wins out. It shares the "pure function" philosophy of Redux, along with use of Immutable.JS and a really powerful notion of functional data transforms/lenses called 'getters'.
Redux doesn't care what you use for state, so you may (or may not) use ImmutableJS too.
Here's an example of the “getters” concept with Redux: https://github.com/faassen/reselect. (Sorry, no README yet :-( ). They don't have to be inside the core.
It's not "Pure" Flux, which is the reason I like it, it doesn't deal with a Dispatcher and it has syntactic sugar for 'common' use-cases, most Rails dev enjoy stuff like that.
Seems like Reflux can't have hot-reloading because there is no (public?) dispatcher to replay values :-/
I wouldn't really recommend Reflux. What advantages it has are shared by other, better libraries like alt or redux, but it has some disadvantages all its own.
I am really enjoying Reflux personally and I think that's one of the good things about React and the Fluxes; there's many mental models to suit different ways of thinking about how to build apps.
There is no 100% correct way to build complex single page web apps but there is definitely a wrong way and that way looks increasing like progressive enhancement sadly...
Docs are incomplete:
http://optimizely.github.io/nuclear-js/