This doesn't seem so necessary or practical.
But if we want to please the OP so she can choose an answer that suits
her, we can't mark similar questions of other OPs as dupes as they
might not be consent with the answers.
This premise is not really correct. The point of an answer is not to please the questioner. The point of an answer is to provide the best, most accurate answer to the question that was asked. If you provide a bad answer because you think it will please the questioner, it can (and will, hopefully) get downvoted. If you provide a good answer that does not please the questioner (but does address the question that was asked) it can (and will, hopefully) get upvoted. The only concern here is for the not as common situation where one person writes a good answer and another person writes a bad answer that pleases the questioner. If the questioner accepts the answer that pleases him, the bad answer will be listed first. There are ways we can attempt to combat this, namely by downvoting, leaving comments pointing out the problems with the bad answer, and supporting these two Meta requests to allow our site to not display the accepted answer first.
Additionally, duplicates are not determined by whether someone is satisfied with the existing answer(s) or not. A question is closed as a duplicate when there is already a post that asks the same question (or a question that includes the new question) and the original post has an upvoted answer. If someone else has the same question and is not satisfied with the existing answer(s), the correct procedure is not to post the question again. Rather the person should leave comments expressing the deficiencies of the existing answer(s), and perhaps start a bounty to draw attention to the question and provide more motivation for people to submit new answers. When you start a bounty you will have the option of including a custom text to explain why you are offering the bounty – use it to say something like "the existing answer(s) fail to address XYZ".
You also say:
So if a question is of "national interest" we would edit it together
as a Wiki to perfect it. It should also be clear, that when one
answers it he meets requirements as of a Wiki article.
All answers have the same requirements and are held to the same standards. Whether the question is of "national interest" or merely "personal interest" we want good answers and we don't want bad answers. Anyone can answer any question (unless it's protected) and anyone with at least 2,000 reputation can edit any answer. Anyone with less than 2,000 reputation can suggest edits to an answer. Community Wikis are largely unnecessary. The main reason for Community Wikis is to make it easier for people to edit answers that are collaborative by design (for example list questions (that don't get closed)). Mandating that "important questions" get Community Wiki answers will reduce a large part of the motivation for people to come up with good answers (as they won't get credit for them).
If the existing answers to "important questions" are sub-par you should downvote them and leave comments explaining the issues. If you can improve the answers with minor edits then you should edit them. If you have a better answer, you should post it and let the community vote on it. If there is nothing you can do with the existing answers and you can't write a better answer, you can always start a bounty (again, with an explanation of what you are looking for). Additionally, you can always start a discussion in Chat if you want input from other users.
Having certain questions marked to stand out as more important will probably not be easy to implement. We can't pin them to the homepage because then new questions won't have anywhere to go. And after a while there will be too many "important questions" to fit on the homepage anyway.
Similarly, there is not much available space on the sides of the screen. Especially with the new designs being unrolled, there will probably not be space for a list of "important questions". At most, we could perhaps fit a link that would lead to a separate list of the most important questions, but then we would still have to figure out how to determine whether a question is "important" or not, which seems rather difficult. (Perhaps a dedicated Meta thread where people can make suggestions, similar to the Best Answers competitions?) In the meantime, your best bet for finding "important questions" (though obviously not perfect) is to look at the upvotes.
As this is a Meta post, anyone can feel free to disagree and downvote accordingly. If anyone has other opinions please post them as answers.