I find the lack of discussion of type systems really surprising in these sorts of discussions and books. Effective use of type systems is a killer factor for me for creating clean, safe, readable and maintainable software designs. When used correctly, strong static type checking make certain kinds of bugs impossible, spare you from writing many kinds of tedious tests that often get in the way of refactoring, serve as…
I do expect the pendulum to swing against type systems at some point soon for the same reasons it swung against OOP: Too much heavy lifting done by something that's hidden from the programmer, encouraging people to be "too clever," etc. Like OOP, algebraic types are a tool that have to be used well, and the current users are people who really like type systems and do use them well. It's only a matter of time before the tool gets into the hands of the average programmer, and then we will see how terribly a great type system can hurt you.