So I think the "mysterious man" is Nanamine still. I'm not quite sure what he is planning to do with all the old mangakas, but since their art style is the same as when they wrote "hits", but the story is more interesting, he must be giving them advice on the story. Maybe he's convinced them to do the same as he was, getting a bunch of opinions from different people, online?

Gah, I can't wait for the next chapter...

Forever lurking...