The chat is a bit more transient but you're transferring messages encrypted again over websocket for example, then decrypted on client.
I'm not seeing what the blocker is, or even issues with scale given its the client side doing the work.
Working example : http://securinote.com/#/notebook/bf528a8d-bf34-4f49-8cb9-e63...
key : embedding
Open up a second tab, make a change, check the network you'll see its sent over the wire encrpted via websocket.