I'm using React + Redux + Koa (+postgresql). The most annoying thing with JavaScript right now is that Babel gives you all ES6 features in your front end bundle, but node 4 only has a subset, so you have to remember when you to stop using features. (No I don't want to transpile back end code).
You can use Babel with node on the back end. See https://babeljs.io/docs/usage/require/. Definitely not the most ideal solution, but it allows you to easily transition into ES6 when all the features land in node.
But neither koa.js nor express.js do websockets. You're holding up a site that would probably be simpler without both koa and express as an example to say that it doesn't make much of a difference whether you choose koa.js or express.js.
Not that this was covered in the article, but it would be a reason to choose Express as the backend. It would be cool to build something similar for Koa though.
I think if you take a lot at the motivations that Dan Abramov had for creating Redux [1], you'll see that improving debugging was at the centre of it. Check out his talk he gave at React-Europe. He basically is talking about improving developer tools. The functional approach Redux takes allows for you to see state transitions and replay actions - making it relatively trivial (compared to say Angular.js) to understand how to reproduce a buggy state.
Dude, this is half the point of redux. Theres a debugger that lets you visually step through every state of the store and your corresponding app - https://github.com/gaearon/redux-devtools
yea, i know, i read it. wasnt much there. already know what all the tools did.... by why jump to this stack from one of the other 15 that came out this year?