He is proposing to use the integrity hash for caching purposes, not for security purposes.
This has been discussed before and it is unlikely it will be implemented as it is almost impossible to eliminate finger-printing and privacy issues if this cache is implemented plus it might lead to security problems:
Whether it's for caching or security purposes, a hash of the contents is a hash of the contents.
The link you shared is about tracking whether a given document is already cached. That's the same problem as with normal caching. At least the top N libraries could be downloaded with a browser update and be equal for everyone.
This has been discussed before and it is unlikely it will be implemented as it is almost impossible to eliminate finger-printing and privacy issues if this cache is implemented plus it might lead to security problems:
https://github.com/w3c/webappsec-subresource-integrity/issue...