Whether or not they are included in a managed environment is generally based on two things:
1. Safety (why RDS doesn't allow certain C extensions) 2. Community/Popularity (Exactly why RDS has PostGIS) A. Demand with a prerequisite of #1
This is very clear. Now tell me: how many output plugins do you see included in RDS. And in GCP's PostgreSQL? Azure Postgres? Heroku?
From RDS:
Logical Replication for PostgreSQL on Amazon RDS
Beginning with PostgreSQL version 9.4, PostgreSQL supports the streaming of WAL changes using logical replication slots. Amazon RDS supports logical replication for a PostgreSQL DB instance version 9.4.9 and higher and 9.5.4 and higher. Using logical replication, you can set up logical replication slots on your instance and stream database changes through these slots to a client like pg_recvlogical. Logical slots are created at the database level and support replication connections to a single database.
PostgreSQL logical replication on Amazon RDS is enabled by a new parameter, a new replication connection type, and a new security role. The client for the replication can be any client that is capable of establishing a replication connection to a database on a PostgreSQL DB instance.
The most common clients for PostgreSQL logical replication are AWS Database Migration Service or a custom-managed host on an AWS EC2 instance. The logical replication slot knows nothing about the receiver of the stream; there is no requirement that the target be a replica database. Note that if you set up a logical replication slot and do not read from the slot, data can be written to your DB instance's storage and you can quickly fill up the storage on your instance.
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I don't see why others wouldn't be available either. In fact, I am not sure why you couldn't use the JSON ones now. (Although I have not tested it).
JD
Also to add, Amazon RDS for PostgreSQL does supports non-core plugins. Wal2json output plugin for logical decoding is supported for versions 9.6.3+ and 9.5.7+ (link) .
