I've updated my post, I've included pre-packed versions for 4 different countries. Each one has the proxy file stored locally, so it should be ok.
By the looks of things, the reason it just says "404" in plain text is because it's just showing you their 404 page. As it's checking:
if(url == 'https://mediahint.com/mediahint.check.js'){ return proxies;
And it's currently returning 404, yet the extension still works, I have a feeling that removing that line will not affect the functionality of the extension. I think all it's going to do (if they ever update the file) is return a list of available proxies and what websites use what proxy etc.
Swap to the dev branch of Chrome. It allows you to enable extensions which aren't from the Chrome web store. Also has the added benefit of having a 64-bit version. I've been using this for a couple of months with zero issues.
Mediahint is not working here too (I'm in Brazil trying to watch US's Netflix). I started using http://hola.org/ that I saw the other day. I'ts working like a charm. I'm watching some trailer park boys in US's Netflix right now. :)