It's an interesting idea, but I don't think we should limit this discussion to hashing. We could discuss the same idea with other encoding/processing schemes.

It's an interesting idea, but I don't think we should limit this discussion to hashing. We could discuss the same idea with other encoding/processing schemes. For example, you can present two or more different bit strings that appear random, but when XOR'd together produces some "illegal" content. Which of these is illegal to transmit?