The problem with approaches like this is that they're prone to false positive/negatives. Take the example above — you could move more payload into the REQUEST variable (say a Cookie header), do more of the array of numbers so no individual token is that noteworthy, you could do something like toss that into a wrapper so someone sees something which looks like (and may actually be) an x509 cert or GPG public key with some misleading comment about that being used to verify updates, toss it into an image or other “fixture” in a test directory a la event-stream, etc.

This is a much harder problem than anything someone is going to come up with in an HN reply on first reaction. People have been working on it for decades but it's especially hard because once a technique becomes popular an attacker can run offline attacks against it and not release their exploit until they've confirmed that it's not detected.