This looks to be a well-put-together implementation of flux. I recently looked over around 20 or so flux libraries to use for a react app I had started, and found only a couple that I liked. I would put this one near the top, but the one I ended up choosing has been great, but no one seems to know about it!
I also decided to use ReactFlux after looking around at the flux implementations. It kind of suffers from the fact no one knows about it but it feels a lot better to use than the other implementations I looked at. I forked the library to support nested objects in the store state and I'm pretty happy with it now.
But I may switch to Marty since I'm not far along with the project and the dev tools look super helpful.
Funny... I actually created some store mixins to do the exact same thing.
I've done it slightly different than you... rather than using `mergeDeep` in `this.setState`, I created some other methods such as `this.setStateAtPath(path, value)` and `this.mergeState` (the latter would use `mergeDeep`)
If anyone is interested: https://github.com/kjda/ReactFlux
It's very similar, but I think I like how Actions and subscriptions to actions are handled with it better.