> Add CREATE ACCESS METHOD command to create new table types (Andres Freund, Haribabu Kommi, Álvaro Herrera, Alexander Korotkov, Dmitry Dolgov)

> This enables the development of new table access methods, which can optimize storage for different use cases. The existing heap access method remains the default.

https://www.postgresql.org/docs/12/tableam.html

Interesting, this could allow purely in memory or columnar tables. A combination of postgres JSON features with an in memory or columnar table would be a great alternative to some nosql use cases.