I agree this should be implemented and I had like to answer some points Thomas mentioned as reason to decline this:
As you pointed out, there's a variety of cases where the warning won't be applicable.
So? It is a warning, not an error. Okay, users may be misinterpreting it, but doesn't that say more about the message being unclear? Why not take this chance to educate users?
If a higher-rep user may be currently editing the clarifications into the post (which as you mentioned is frequent). Odds are the edit we asked the new user to make will end up discarded.
Again, not a reason to not show a warning. The warning gets shown before the user adds a comment, not afterwards, so there is nothing to edit yet. And even if a user was editing already, what is the point? Doesn't that happen all the time? How often am I halfway editing a post while I receive a notification someone else already edited? This is just a fact we should accept.
It might not be obvious to a new user what the warning is asking for (although this is something we might be able to address with copy).
So make the notification clear. Link to a FAQ that explains it all. Show examples of good and bad there, and a user will understand.