Developers of real-time apps and underlying infrastructure spend considerable time engineering ways to proliferate state changes to and from clients. It might be helpful if the database would take care of this.
Martin Kleppmann posted about a talk he gave about apache sanza and the notion of an “unbundled db”. One key rationale he gives for his proposed db architecture is to better facilitate clients being able to subscribe to data changes (as opposed to the querying / polling that traditionally occurs in apps).
Kleppman cited RethinkDB’s changefeeds as an example implementation, as well as websocket services such as meteor.