According to Mozilla:
The HTTP Content-Security-Policy
require-sri-fordirective instructs the client to require the use of Subresource Integrity for scripts or styles on the page.
I fail to see the benefit. The SCP is designed to protect me from someone injecting scripts into my page. If an attacker is able to inject a script tag, wouldn't she also be able to inject an appropriate integrity attribute?
What attack is possible without this directive, but fails with it?