Postgres already handles JSON well. MySQL does a good job now too. And there are tons of other JSONb/document-stores like Couchbase, CouchDB, RavenDB, MarkLogic, ElasticSearch, ArangoDB, CosmosDB, AWS DocumentDB, and even RethinkDB that still exists.

It's a nice goal but there's likely not much of a commercial market for it, if that's your roadmap.