The Watchtower need to keep coming up with new light, it's totally necessary for them in order to maintain control.
I remember the reaction of several elderly JWs to the 1995 generation change. They had been in the organisation for years, getting older without any real sign of the new system that would make them young again coming, but confident that the generation doctrine as it was then would ensure that it would be here before the end of the 20th Century.
All that changed in 1995, and all those old, faithful sisters and brothers suddenly realised that they might die in this system after all. I wasn't overly thrilled with the change myself, but some of the older ones were very near devastated, though the Watchtower are so clever in the way they change a doctrine that most of them accepted it.
Now that I'm no longer a JW, I can see these changes for what they really are, ways of avoiding the embarassment of having to explain another failed prophecy or, as in the case of the change in the gathering of the anointed in May, having a ready-made excuse for the number of Memorial partakers rising. This latest proposed change won't be the last time the Watchtower tinker with the generation doctrine, of that I'm sure,
They'll probably say it's Jehovah'w way of feeding his people spiritually by gradually increasing their understanding of his word, when in reality it's a desperate act by increasingly desperate men who are well aware of how much opposition they have nowadays, and are fighting to maintain control of the millions that they have fooled with their false doctrines.
Marion