I think the reason for the overlapping generations is to put a new deadline on the generation teaching. Increases have been slowing and non-existent in some lands. If you look at the history of JWs, there is a significant bump in membership whenever there was a looming deadline- 1925, 1975, 1980s, & 1990s.
The 1995 "understanding" of the generation was too broad and basically gave no timeline for the end to come. Combine this with the relaxing of views on higher education and it's easy to see why the increases slowed significantly (the internet helped too, of course). With the new understanding, this GB have put a new deadline on the "generation" (around 120 years from 1914) and have stated that the 2nd group of the "overlapping generation" is advanced in age. Combine this with the increasing restrictions on higher education and it's easy to see that they are ramping up the urgency to push more hours out of JWs and increase membership.
I don't think they will change the generation teaching until the clock runs out or almost runs out on the current teaching (around 2034). The SOP of the last few decades is to only change an "understanding" when it is clear that the current "understanding" is no longer valid. Changing it back to the idea that it is just the anointed would remove the urgency just as the 1995 change did.