We built a remote (and encrypted) data sync spec for graphs, it can be used for both traditional table (relational) and document storage as well as key/value data ( https://github.com/amark/gun). It has push built in and is fully decentralized and running in production today (terabytes of traffic), and handles concurrency and offline conflicts out of the box.

There are some half baked GraphQL query engines for it as well as some SQL query prototypes on top, but not quite ready yet. What were you wanting to build?