There's no reason to add this. The existing close reason "Exact Duplicate" already covers this case. I think that the full text of the close reason is quite relevant here, and also very clear:
This question covers exactly the same ground as earlier questions on this topic; its answers may be merged with another identical question.
There are two parts to this: first, the part on which you are focusing, that the questions themselves be equivalent, and second, that the answers can be usefully combined. You're completely ignoring the second half. Your comment below that "the full text of the close reason is irrelevant" absolutely boggles my mind. You also say below "There's no way around what the title of the close reason is!", but the title of the close reason is just a title, not a rationale -- it's not even a complete sentence.
Grace Note's example is excellent (as is the whole of the quoted post). Identical answers to two questions do not ipso facto cause the questions to be duplicates. This has been said in other places, and I completely agree with everyone on this. However, the solutions to the question do have to be taken into account. There were a rash of questions the other day in objc that were superficially different:
These all have the same root cause, despite each having its own particular take on the problem. (There are plenty of others floating around, too; maybe one calls
sleep(), perhaps one uses a
UILabel and the other a
UITextField.) The answer, and the underlying issue, is identical in all cases.* In other words, they "cover exactly the same ground". They should be closed as duplicates so that one authoritative answer can be established, polished, and referred to whenever the next person has this difficulty.**
An important point here is that the asker of a new question doesn't have to know beforehand that the other question applies (as long as the explanations on the other are sufficient to cover the new one). Two people asking about
float arithmetic and precision might not see the connection between their questions, but the explanations are very likely to be usefully equivalent. Which leads me to your statement:
When a question is closed as an exact duplicate, it is a reprimand to the asker
I strenuously disagree with this. The act of closing (especially as duplicate†) has little to do with the poster, and everything to do with the maintenance of the site.
Closing a question as a duplicate of an earlier question benefits everyone. The asker still gets an answer, future searchers can find the information they want in a single place rather than having to comb through three dozen different pages, and regulars don't have to rehash the same questions and answers over and over. As time goes on, the answers on the linked question accrete more information, so that their worth only grows.
The web at large already provides a million variations on the same answer to the million different ways to express any given problem. One of the most valuable features of StackOverflow is that all the question variations can be pointed at one most comprehensive and useful explanation.
In short, I think that the problem you have identified is not actually a problem. Questions whose causes are identical, and which therefore have equivalent answers, can already be closed as duplicates.
*You can see this if you read through the answers, although of course it may not be completely clear if you're unfamiliar with the framework.
**Cf. the blog entry The Wikipedia of Long Tail Programming Questions
†When a question is closed as NARQ or Not Constructive, it incurs an auto-downvote. Notice that this is not true of "Exact duplicate".