What makes this community. Is it the questions and answers or the people?
I would limit the functionality to promote some thing to a question to some one who has a high reputation. As has been pointed out, people who ask question's in the answers section would most likely be passing through and not contributing to the community.
So to answer the question above. Its the people who make the community. If some answer really needed to be turned into a question let some one in the community who understands that it needs to happen do it. Does that mean we need to create functionality like migrating an answer to a question. Maybe, it could make it easier for the community to create those questions and accept an answer. A quick look at the number of unanswered questions makes me think that we will just be increasing that number significantly. I don't think people will be taking responsiblity to accept an answer and provide feed back on the problem check out this question and answer to see what I mean over 20 comments. This is what makes stackexchange, SO, and the other sites work. Its the people.
If people are not using the site in the way it was built is? Is it because it is difficult to understand or because the are not really interested in the community. If they are not interested in the community should the community really take up the slack and do a lot of extra work trying to maintain all those extra questions. If it is because the site is difficult to use and understand that is a septate problem.
May be some stats on the number of answers with comments which propose that the answer should be posted as a question would be helpful to understand how big this problem really is. I don't know how to do this type of query on the SO database. May be some who who works on the SO site could do it. May be this post need to be turned into a question.
About the site being difficult to understand, I think we / stackechange / SO have taken a very narrow view of questions and answers. A question should be concise and have one possible solution? This is ok for most questions but there are some that need more explanation and deeper answers. Which community wiki provides the functionality or as posted above active member participation. This post is related in the problem that is being talked about here. How answers and questions should be viewed.