[sublinear]

I know this is just a game that never ends, but if they're already rewriting the HTTP requests what's stopping them from rewriting the page contents in the response?

SRI is for the situation where a CDN has been poisoned, not this.

[DoctorOW]

It might not explicitly be what SRI is meant for but it'll narrow the proxy's options to:

A. Blank page

B. Let the find and replace update the CSS. Generate new hashes in the HTML.

C. Find someone new to pick on.

B is time and potentially computationally expensive, so it makes C a better option.

[sublinear]

A doesn't work because B doesn't prevent the attacker from regexing out the hash altogether and changing the domain name in the tags to their own.