There are a whole bunch of people who claim copyright on those files; their names are listed in the files' headers. I'll note that when I requested copyright assignment, I alerted the clerk that I was using these libraries. The plugin doesn't work without them.
I could probably externalize those files into an "npm" package and instruct users to install a separate executable to run the JavaScript portion of the plugin. But I'd much rather just include them in the package, because then it "works out-of-the-box".
As for ert-async, what would be our course of action if he does not agree? Will we add a copyright exception, or will I not be able to include the file in the repo?