Immutable.js isn't a peer dependency. But it's often used with it. And even if you don't use an immutability library, you end up programming in a way that accomplishes much the same thing.

This is a tremendous amount of progress for a first pass.

Like @wacii said, immutable is not technically a peer dep; immutability is kind of required for Redux. We can do immutability manually by deep cloning, but it's
a) easy to forget, especially for newcomers/people not familiar with Redux
b) leaves state objects open to (inadvertent) manipulation in code; anyone can push onto an array/set/delete a property, in ways that could potentially break code

It is a different way of coding and can take some getting used to, so we can definitely discuss this more if you're not comfortable with it.