If nothing else it would make a great twist in a fiction setting.

These paraphrasing instructions could be followed. But the paraphrasing could be done using some LLM. A sufficiently advanced adversary manages to invert the model somehow, and as a result can get the original plain text out of the paraphrased message, which lets them do a known-plaintext attack, get the key, and use it on other messages.

Sort of technobabble (is the idea of inverting an LLM nonsense?) but fun.