Given that Rob Pike embraces neither OOP nor functional programming, one has to wonder what he really means by composition.
The closest thing to composition or reuse in Go are the typeclasses and it's pretty weak. I hope he enjoys specializing his maps and reduces for every type instance.
Rob Pike has in the last few years spent a lot of time complaining about the younguns and the slightly less young younguns, but I've not seen him talk in concrete terms about what he thinks the solution is.
Other than, "use Go", which doesn't actually answer the questions that are raised by his complaints. Like how Go somehow supports composition in a superior way. I've spent some time with Go, built a few projects and services. I wasn't impressed.
I'll just keep using Clojure and Python until Pike starts talking about what he actually means to do to solve these problems.
Hickey is an iconoclast too, but he's sensible enough to stay focused on what can move the profession forward as opposed to complaining profusely on Google+ every other week.
If you really want to learn something interesting, you'd be better off learning about the fundamental relationships between code, data, state, and objects such as Hickey has covered in his past talks.
They're enlightening even if you don't care about Lisp and the talks themselves aren't really in terms of Clojure except to explain how it does things differently.
