Related to Why is our answer rate so low? and Improvement Drive - Cross Validated on meta, there are many one-time users who post a question just because they need an answer for a particular problem and then they vanish again. It seems to happen quite frequently that such questions receive an answer some time later but probably the OP has already given up on waiting for one. Except from discouraging answers to one-time/low-reputation users, I could also imagine that new viewers looking up such a question may incorrectly conclude that the provided answer is not useful just because it was not accepted.
To raise acceptance rates and to promote good answers also to older questions or to questions from one-time/low-reputation users I would like to discuss a voting system for senior users (2k reputation, for example) to accept answers instead of the potentially inactive OP.