Subscriptions: OJS 3.0.2 does not yet include subscription support. That’ll be released with OJS 3.1.0.
Simultaneous editing of documents: we’re working towards this using an integration between OJS and the Substance Editor, and OSCOSS (another group we’re familiar with) is working towards this using Fidus Writer. Neither of these is at a production level yet.
RSS Feeds: OJS 3.x already has the Web Feed Plugin built in, which generates Atom/RSS feeds of the latest-published content.
Regards,
Alec Smecher
Public Knowledge Project Team