Yes, but how do you conclude without a doubt that what was hashed hasn't been tampered, leading a site to believe it's legal or malware-free content, while it actually isn't, and you've just been fed a shadow version of the real thing. We can reach for consensus algorithms, but ultimately without something like Van Jacobson's Content Centric Networking, it will be very hard to prove with enough confidence for a judge to make a ruling.

1. Because the hash is in the blockchain, certificates cannot be created retroactively.

2. The notary could make their archive public, so that any interested party could go through and verify that it is legit.

3. By using many different notaries the chance of any one of them being bad would be reduced.

Sure, and if the quorum consists of 6 members, and you managed to undermind 3 of them by making sure they're fed the same custom shadow content, you'll have a split.

You could literally put it in the Bitcoin blockchain. This will be spread among thousands of machines with cryptographic proof.