Right now engin.io provides backend (database access and user management) only. A very desirable feature would be to provide a way to exchange peer-to-peer communication through WebRTC with engin.io. While any sort of exchange could work, and such and exchange could be accomplished with current facilities, WebRTC is standard, and providing a way that could interact with both browsers as well as Qt applications would be desirable.
QtQuick doesn't provide out-of-the-box support for WebRTC, but QtWebEngine does. Even so, it's most desirable to have QtQuick setup data streams and video/audio streams, so a QtQuick module to setup a WebRTC data stream, audio stream, and audio/video stream should be created as well.