It's quite interesting that those events are happening at the same moment. I wonder whether they are related
I think there are multiple separate events here, timed to coincide in order to minimise disruption. It's hard to be sure whether they share overlapping causes, but I'd guess that there's at least an element of that.
Yes. In public relations you never want to trickle out bad/concerning the news, you want to "rip off the band-aid and preferably follow it up with some positive/distracting news like 3.5 Pro model release or price drops.
Isn't it "just" a matter of Jeff Dean (& co) leaving, Hassabis replacing Dean, and Kavukcuoglu replacing Hassabis ?
A massive shake up for sure, but why do you see it as separate events merely timed to coincide ?
So there are two events here:
Event 1 - Jeff & co leaving.
Event 2 - Demis stepping down. DeepMind doesn't need a "chair" and "Alphabet's chief scientist" is a bullshit title that Jeff invented for himself when he moved from Google Research to GDM, to make it look like we wasn't abandoning the former for the latter.
The third change is basically ratifying the status quo, since Koray has been de factor running GDM for a while now (and directly reporting to Sundar in addition to reporting to Demis, who in turn also reported to Sundar - quite some triangle there).