This solves the problem on the server side, using existing standards, without building any new tech into the browser.
The suggestion solves that issue by using hashes of the files, so it doesn't matter if they are loaded from a remote/CDN URL or from the same server, they will be considered cached by the browser (and loaded from cache) regardless once the hash matches.
> It turns out that many websites are loading content from Google’s CDN, or Facebook/Twitter APIs, which are blocked in China.
Using a hash would allow you to load them from any URL, including the blocked ones.
But, you know, you live in the US and your solution works for everyone in the US, so F everyone who doesn't.