In one of the other HN threads on the issue, there was mention that the switch occurred shortly after a change in leadership position of individuals with enough 'power' to impart technology changes by decree. So there is an aspect that there was some, if not much, political opinion involved as there was any technical analysis involved in the change.
Given the fact that the change which occurred is an "apples to oranges comparison" change (PostgreSQL and an SQL normalized DB table structure to MySQL and a noSQL style single table key-value store) then there is some credence one can put towards the rumor that some (or most) of the change may have come about from a PHB [1] saying "do this, this way".
Considering some of the things they wanted to improve were presented almost a decade before as problems (along with technically sound solutions to those problems), I actually think they did the best thing they could for the Postgres community.
actually I watched the video and the errors happend here are more cultural errors.
I guess the switch is more like a "we failed, so we start new".
and new means with something different.
also their replication strategy looked like a joke and not enough automation. hopefully they never use galera, else their bad engeering practices could actually suffer in huge data losses.
I've once run galera-cluster and it pretty easy came to data losses especially after short network splits which occured randomly at the network.
