I think 10 years from now, there will be a great turnover rate. There very well may be the same amount of witnesses, but many of them will be different people than there are today.
Some current witnesses will see the light, and leave. Perhaps at some point the WTS will lighten its viewpoints regarding such strange beliefs and attract others.
But the most likely, is the same amount of people as now, with some dropping out, and the replacements being the kids. Just like now.