OK so probably it should be clarified that the author has a great blog on PostgreSQL including a series called "Waiting for PostgreSQL $VERSION" where he talks of highlights in the edition that would only appear later at the time of writing. Looking back, these are interesting descriptions of prominent changes in the next few releases, and most of these entries are still valid today, i.e. most features didn't change much.

Oh, thank you for providing clarification. It is indeed quite interesting to read. I see the author already has an article for pg 17

Should be marked 2021. The current release version is 16 with 17 now in beta.

Since many (most) are not updating with every release, it's still valid as an update too. E.g. the supported PG version of Centos 7 vs the base version after going to 8 or 9 and so on.