LGTM!

Generally lgtm. Any thoughts on whether we could/should have a way of clearly indicating which reducers expose Immutable objects vs. JS objects?

@Bjvanminnen perhaps a naming convention? I would say prefix everything with immutable but that is too long. Perhaps postfix with the specific immutable type? So this would become state.screensMap.get(...)

Another option (that I don't think I like) would be to put immutable reducers in their own subtree, i.e.

state = {
  instructions: { ... },
  immutable: {
    screens: Immutable.Map({...}),
    somethingElse: Immutable.Map({...})
 }
};

It's also possible that we don't need to do anything here, and it will be reasonably clear just by looking at the reducer or other consumers of the reducer whether or not it's using Immutable.

going to just leave this in my applab import branch