> The scenario that worries me here is somebody using a bleeding-edge PGDG > server package in an environment where the rest of the Postgres ecosystem > is much less bleeding-edge.
If someone installs a postgres RPM/DEB from postgresql.org, they could also install postgresql-jdbc, right ?
No, this is not how the majority of people use Java at all. They would use Maven to pull down the JDBC driver of choice.
I would guess there might be some distro specific java apps that might actually use what is on the machine but as mentioned any reasonably complex Java app is going to ensure it has the correct versions for their app using Maven.