There's a ton of room for improvement in the architecture of relational databases. This isn't a dig against Postgres, or ignoring how difficult it will be to get a new system to the same level of maturity. But databases designed natively for cloud/clustering, SSDs, (pmem soon perhaps), etc are quite a bit different. There's enormous simplifications and performance gains possible.
There's been a lot of exciting work in this area over the last decade or so. Andy Pavlo's classes are great surveys of the latest work: https://15721.courses.cs.cmu.edu/spring2020/
CosmosDB is an example of a relational (multi paradigm properly) database with a quite different architecture vs the classic design, that's moved into production status quite rapidly.
FaunaDB and CockroachDB are moving with solid momentum too.
There's been a lot of exciting work in this area over the last decade or so. Andy Pavlo's classes are great surveys of the latest work: https://15721.courses.cs.cmu.edu/spring2020/
CosmosDB is an example of a relational (multi paradigm properly) database with a quite different architecture vs the classic design, that's moved into production status quite rapidly.
FaunaDB and CockroachDB are moving with solid momentum too.