Sorry for the late reply. Multiplexing is not a panacea, there's still some overhead, and even if there wasn't there's still a point where you start to lose lot of performance by limiting gzip compression (the smaller the file the less efficient the compression is).

You can read more about why we'll always need a bundling step at the following links:

http://engineering.khanacademy.org/posts/js-packaging-http2....

https://medium.com/@asyncmax/the-right-way-to-bundle-your-as...

https://medium.com/webpack/webpack-http-2-7083ec3f3ce6#.74q6...