This question is primarily opinion-based, but someone can develop a very reasonable answer.
Should we leave it open?
I would disagree that it's an opinion-based question. While a good source for the data is hard to come by, the question itself is very objective.
The three answers it has received so far seem pretty on-point. Chris Lively's answer is certainly subjective, but not opinion-based.
RualStorge's 4th section should probably be removed, as it wanders away from the question. However, I'd leave that to him as a comment for him to consider.
I would side with leaving it open, and pruning any answers that appear that focus on the merits of open wage structures, rather than answer the question about their occurrence rates.