I think we may see actual decline within the next couple of years. Last year's worldwide growth was only 1.5% which must be one of the lowest growth figures ever.
A key indicator may be the age profile of JWs. I've only been to two meetings in the last three years but it struck me how old everyone is now at the Kingdom Hall. It's the same people just getting older. There is no new generation, or very few, coming up to replace them.
The results from the Pew Research Centre show JWs getting older between 2007 and 2014. It's a well studied phenomenon that an increasingly older age profile of religious groups and decline in numbers go hand in hand. And the increase in average age often precedes the decline phase and then proceeds in tandem with it. On this basis I think that JWs will soon begin to decline and that their average age will continue to increase at the same time.
What I think will be really interesting to watch is how JWs manage decline. How will they cope with it psychologically, considering they've long claimed that growth in members was the reason Jehovah is delaying Armageddon. How will they cope organisationally with closing congregations and consolidating. In fact they are already doing that. But the process of losing congregations may speed the decline further.