What an excellent thread.
This has been an issue for the WTS for some time now, and I can't see it getting fixed any time soon. One of the first KM schools I went to when I was an MS talked about the elder / MS ratio in New Zealand. There was almost double the number of elders as there was MSs. Ideally, they stressed, it should be the other way round so there are plenty waiting in the wings to help and assist the elders and then get promoted and ease the workload on the body, and let any older elders cruise.
That was eight years ago.
In my time as an elder we always had the same issue when the CO turned up. In the pre-meeting to discuss who we would put forward to the CO as potential MSs or elders it was always the usual suspects. None of them had changed anything since the previous CO visit when they weren't appointed. They all moaned that they weren't getting advanced, yet never bothered to implement any of the suggestions made to them.
It is reasonably common to have sisters doing some non-teaching roles in the congregation such as accounts and microphones. They will always be under the 'supervision' of a brother though. This may become more and more common as time goes on. I doubt we will ever see the day where a sister is giving a public talk though. The penis means power, and the Old Boys Club will be sure to keep it that way.