I read the changefeeds post, but I don't think I understood exactly what they're for. Would clients be talking directly to the database, or would a persistent app worker block on database updates and then send this to the client?
You can see an example here of a node.js app using a changefeed to convey updates to the frontend through Socket.io: http://rethinkdb.com/blog/realtime-cluster-monitoring/
Though, of course, you can also build things other than web apps. Here's a simple IRC bot built with Go that also uses RethinkDB changefeeds: http://rethinkdb.com/blog/go-irc-bot/
The app can then also have a persistent websocket connection or whatever to the client, so you're able to get push architecture all the way from the data source to the client.