HMR is kinda finicky, and require.context is finicky as well. When debugging HMR/require.context code that doesn't work I usually start with a known working version and then turn that code step by step into the code that isn't working and then watch when it fails. Here's a working version for those of you that want to do the same thing, or just want to play around.
This is what should work: run
npm install and then
npm start. Open http://localhost:8080/bundle in your browser. Open the console. Now edit or add files in the filesToLoad directory.
If you want to create a module that does the hot reloading and that your code can then subscribe to check out the allow_import_of_hmr_module branch it's a bit more complex, but arguably a better starting point for actual code.