Earlier quoted context omitted.
I don't think it would be fine. Someone's actual writing (or talking) is a rich stream of information about who they are, their motives, their preferences, modes of persuasion, and so much more. Undetectable LLM writing essentially allows someone to assume another person's identity. That is not good for anyone except the person trying to pull off a "scam" of some sort, in the broadest sense of that term. It's bad for…
Good for privacy and productivity.
"Productivity" is not. It's only good for fake productivity. The consumers of the product will almost always be better off with you disclosing what the LLM did, and what you did.