There are many questions where users post an initial, incomplete question, which can not be answered without more information. For example, they post a question about a error/issue with their code/query/... but do not include their code, or it's missing relevant parts.
In the issue queue on Drupal.org, we have a status called "postponed (maintainer needs more info)". I use that often because it allows me to move issues which are impossible to resolve with the given information out of my way.
I think something similar might make sense too here. It could save a lot of time for those which are browsing through unanswered questions looking for something they can answer.
The easiest way to do this would be a new tag, called "needs more info" or similar. When seeing that tag in the question lists, you know that you don't need to look at it. However, AFAIK, it is not allowed to use tags for meta-information like this. And it doesn't allow advanced functionality like informing the question asker (by sending them a mail or a on-site notification) about the problem, auto-closing such questions after n days or hiding such issues from lists by default.
The downside is that it could possibly be used incorrectly, e.g. when question is flagged for this incorrectly and then nobody looks at it again. But it might be possible to solve that by automatically removing that meta-information when the question asker edits his question.