Down-voted questions seem to fall into two categories: fixable and unfixable. Some questions are just inappropriate, easily answerable with minimal search effort, or have other problems for which nothing will make them good questions. Others are, or can be, good and useful questions but were asked poorly. Downvoting is supposed to be an incentive to improve the question.
There is a consequence, though--the downvotes don't go away when the problem is fixed. They served their original purpose. However, now you have a perfectly good question that is stigmatized by the downvotes, discouraging viewers because the downvotes are then misleading. You can also have the situation where people spend time answering the question and before the answer gets any upvotes, the OP deletes the question due to the downvotes. This disincentivizes answering.
It seems like it would be beneficial to have two types of down votes for questions. The new one would be a conditional downvote. It would be available to be cast (voter's option), in instances where the voter's objection would go away if the question's problems were fixed.
There are a number of ways the mechanics could work:
The voter gets an inbox message that the question was edited. If they are satisfied with the change, they un-downvote.
There is some type of community review where conditional downvotes can be removed if the problems are deemed fixed (conditional downvotes would be used in those situations where the problem is easily recognized and the voter is OK to let the community decide).
Both approaches would benefit from some delay (maybe 12 hours after the first edit), since improvements to questions are often done in several rounds. These two approaches are not mutually exclusive and there are probably other potential mechanisms.