It is outside the scope of any RFC to tell someone what they must put in the body of a message. It is foolish to expect that someone will not simply delete the text that they did not write themselves, just like many people modify or remove the attributions that their agents put in for them. If YOU want to put something in the body, go ahead, knock yourself out. Demanding that others must do the same is not in the scope of this group. If you don't know what the header means, read the RFC and learn.
Old dogs can learn new tricks.
That's what the proposed headers prevent. If the sender hasn't deleted it, or if his message included it in the first place. The person you answered has a very good news server, and does not accept news discussions in his email. He has set his software to prevent him from having his time wasted with news things in email. YOU are deciding for him that YOUR message is so important that it must be dealt with at email priortity instead news priority.