IMHO, user databases (both CouchDB and PouchDB) are just front cache. User can mess with his data in CouchDB/PouchDB using API, so it's important to keep data in an inner database, inaccessible to user, and copy data between databases. Inner database can be a SQL database, e.g. PG with jsonb.
+--+ +-------+ +-------+ +--+
|PG+<-+->+CouchDB+<-->+PouchDB+<-->+UI|
+--+ | +-------+ +-------+ +--+
|
+->...
|
+->...