As I read it the new mag makes clear that at this time the official explanation is not multiple overlapping generations but two. Now granted it could conceivably be stretched further to include another generation but that will have to wait until this one is spent. Right now it is just two generations, the "old" annointed and the "new" annointed. (Or more specifically the old leadership and the new leadership.)
The numerous changes to generation pre-1995 were prompted by time constraints due to the growing gap from 1914. However, the two previous changes expanded the time indefinitely. This new change was not prompted by a time crunch as they had already detached a single lifespan from 1914. So what are the reasons?
From Barr's talk you can see that this new generation teaching renews that sense of urgency that the pre-95 teachings had. It gives you a group to look at, the current "young" Governing body, and start watching them get older and older, knowing that the end will come before they all die off.
But I think there is more to it. If you take this change in teaching with the general tone of the Watchtower of late, there is a real sense of the Governing Body seeking legitimacy. The new generation teaching acts is sort of a passing of the baton, from the former group to the new. That is also the importance of Barr, one of the old guard, giving this talk at the annual meeting.