goog.module is a new way to define Closure namespaces: https://github.com/google/closure-library/wiki/goog.module:-an-ES6-module-like-alternative-to-goog.provide
It is used for example in https://github.com/google/incremental-dom
I didn't do full check of how Closure libraries are handled, but one function which is definitely used by cljs.closure is cljs.js-deps/find-classpath-lib which calls cljs.js-deps/parse-js-ns to read a JS file and parse module information from it. Currently the function reads lines before first function declaration and uses a regex to find goog.provide and goog.require calls. Probably Closure Compiler has some built-in functionality to parse files which could be leveraged.
Besides reading module information from files, another question is if using goog.module defined namespaces for traditional/legacy namespaces generated by ClojureScript compiler needs something special. When goog.module is required, goog.require returns the exported object but no global is set. There is however a function to create the globals: https://github.com/google/closure-library/wiki/goog.module:-an-ES6-module-like-alternative-to-goog.provide#how-do-i-use-a-googmodule-from-a-traditional-closure-file
Can we still assume that goog.requires all occur before first function declaration?
Would be fixed by using possible Closure Compiler functionality
"GCL hasn't switched to it so it may be something driven by some users not something that Google uses more broadly" (David at slack)