Personally, I would say that still reeks of being manipulative. I've received messages from a friend which were definitely LLM-generated, it made me like that person considerably less

If they use the LLM to search ("when did X tell me about that party somewhere around Y's neighborhood") then I don't think there's any problem.

If they configure it to indicate a prefix, for instance when answering questions like "when are you free to hang out" and it responding "[AI] according to X's calendar and work schedule, they may be available on the following days" I might also consider that somewhat useful (I just wouldn't take it as something they actually said).

If they're using LLMs to reword themselves or because they're not really interested in conversing, that's a definite ick.

I would personally use such a system in a receive-only mode for adding things to calendars or searching. But I'd also stick to local LLMs, so the context window would probably be too small to get much out of it anyway.