Although mostly anecdotal, it certainly does appear a tipping point has been reached. Much of what I am hearing, (and I am quite far removed from the JW scene, so my data on this is very limited, admittedly), has finally brought me to a point where I no longer trust the numbers the society is printing. I have held off a long time from saying that, however I now would say that they are spinning the numbers positive anyway possible. They have a lot of latitude to do so, since the way they account for members is far from any standard any other religion uses. For example, since no one really knows if by "publishers" the WTS refers to baptized only, or unbaptized publishers as well, this could easily be an area they adjust behind the scenes and no one would be the wiser. There are many other "tweaks" they can perform to the accounting process that would also allow them to spin things positive for a while.
It seems most "normal" JWs left are extremely apathetic, or awake but leading double lives for family reasons. Many of the latter group are too scared of the consequences, (and there are consequences), to come forward openly. I think this is a much larger group than most people realize.
As far as the apathetic go, this is a very large group that can be pushed mentally out given sufficient reason. This was me for several years before I left, so I know first hand apathy is almost always the first step to becoming mentally free for most. I know a former congregation I attended has lost about 33% of its membership over the last 20 years, and mostly only the very apathetic, (apart from a few kooks, I am sure), are left.
That only leaves the mentally/emotionally unstable left. Long term, this brain drain will kill the WTS. The pace of decline is accelerating rapidly. This is consistent with a critical mass or tipping point being reached. Time will tell how long it takes.
d4g