I do think it could be neat with the support for a tag for "this is can be cached" in TLS streams, which could be applied to privacy unsensitive material, which identifies the ciphertext blob and thus lets the ISP tell the server sending it "I'm now going to cache this blob, tell every client on my network to use the same decryption key for this blob for X time and I'll hand them my cached copy".
Presumably you'd have to use a signed hash of the ciphertext as the identifier, and decouple the encryption of these blobs from the rest of the TLS stream (use independent key material) to ensure it remains secure. But this way, any ISP that sees the same blob appearing frequently can chose to cache it automatically and quickly start saving bandwidth.
Also, for maximizing privacy, I think this tag should be applied by the client only (can be disabled if you want to reduce metadata leaks) when the server tells the client "this particular data with identifier X can be auto-cached on the network level". One potential neat advantage here is that a LAN router/proxy could implement a cache for its own nodes by having the nodes send these cache requests directly to this router instead of letting the ISP see it, so you don't leak this metadata outside your own network.
Presumably you'd have to use a signed hash of the ciphertext as the identifier, and decouple the encryption of these blobs from the rest of the TLS stream (use independent key material) to ensure it remains secure. But this way, any ISP that sees the same blob appearing frequently can chose to cache it automatically and quickly start saving bandwidth.
Also, for maximizing privacy, I think this tag should be applied by the client only (can be disabled if you want to reduce metadata leaks) when the server tells the client "this particular data with identifier X can be auto-cached on the network level". One potential neat advantage here is that a LAN router/proxy could implement a cache for its own nodes by having the nodes send these cache requests directly to this router instead of letting the ISP see it, so you don't leak this metadata outside your own network.