SQL equivalent to CouchDB for 2 way replication
The way CouchDB's replication mechanism is created and integrated is kind of unique. This has to do with the historical situation, that CouchDB should be able to live in a distributed world from the beginning. That said, "older" databases like MySQL or PostgreSQL do not have these features, because there was never a need for it.

It is very important to understand, that MySQL and PostgreSQL do offer replication but not in the way CouchDB does. There is MySQL Percona and PostgreSQL BRD but one has to go through a more time consuming setup process in comparison to CouchDB where you simply add a replication document with the source and target in the _replicator database.

So as far as I know, it will be difficult to find something comparable to the mechanisms and features you are looking for.