I don't think that many people switched to MobX to be honest. It's very similar to knockout observable and while it works, I don't think I would use that approach again. I suspect people like the familiar OO syntax of MobX. I can't think of advantages it has over plain old streams (most.js, flyd.js)

I've just finished my first major redux project and found it incredibly slow to develop with. Write an action type constant/action creator/dispatch/reducer/mapStateToProps just to show an element in response to a mouse click? I found myself cutting corners on the UI because the amount of code I'd have to write makes it seem like a huge task.

I'll be evaluating mobx for my next project, definitely, along with Relay. If I can maintain the same view-as-a-function-of-state approach of redux while writing less code, I'm sold.