I honestly don't think that there is anything they could publish which would provoke a 'mass exodus.
I agree. To understand why, let's look at the reasons why most join and/or remain in the religion:
1. People who buy into the theology
The centerpiece of modern JW theology is the organization concept, i.e., Jehovah deals directly with an organization and only those who belong to such organization will survive Armageddon. A corrolarly to that is the Jehovah-knows-better-than-you doctrine. Regardless of how nonsensical a doctrine or idea may seem to you (think of God's command to Abraham requiring him to sacrifice Isaac), Jehovah (through his "organization") is always right. Therefore, honest-hearted JWs will swallow their doubts and quickly embrace whatever nonsense is thrown their way. It's known as mind control to the rest of the world.
2. People who join and/or remain in the church for companionship reasons
My mother is one of the least intellectually-curious persons you will ever meet. If you show her a map or talk to her about history, she will cringe. She doesn't like to be bothered with that type of stuff. She joined the religion because of how well-behaved she perceived JW children to be. She was impressed. She was an immigrant woman raising her kids in a foreign country where she didn't speak the native tongue. All of a sudden a well-dressed couple approached her and invited her to a religious service where the children were all dressed up and stayed in their seats for the entire two hours. That was proof enough for her. She signed up as soon as she could. That was the environment in which she wanted to raise her kids. She couldn't explain to you what it is exactly that Jehovah's Witnesses believe with any detail, but that's not what motivated her. The companionship/familial aspect of JWism is not affected by their constant rewriting of doctrine.
3. People who join and/or remain in the church for family reasons or for fear of being excommunicated
Many, if not most, of the born-ins fit this category, especially those whose entire extended families are in the group. To be excommunicated would mean being cut off from most everyone you know. You would have to spend years creating a new life for yourself. Freedom from JWism is simply not worth the cost to many of these people. Therefore, there is an entire sub-culture of young two-face JWS, especially in large cities. These kids go through the motions and do what is expected of them superficially, but behave in a completely different manner when they're by themselves. A change in the generation doctrine is not going to make the price of leaving the religion any more bearable.
4. People who remain in the church because they dedicated too much of their lives to the religion and realizing they were deceived is too much to bear.
This encompassses people who spent multiple decades of their lives in the church, who married someone who was "spiritual" but whom they didn't love, who gave up a college education and/or a good job, who chose not to have children in order to dedicate more time to "the kingdom interests," etc. To come to the realization that you spent your life in pursuit of man-made rules and that there will be no reward for your sacrifice is simply unbearable. As a protection, the mind simply discards any evidence that the WT is wrong. The thought of having to face that reality is simply not worth it to a lot of "old timers." Changing the generation doctrine once again won't make the process any easier to bear. Besides, these folks have seen the WT undergo much bigger changes.
So, in sum, I agree with you. I fully expect this newest change to go un-noticed by most JWs, at least publicly.
