Is it possible to use WebRTC Data Channels on Node.js in a way that mimics the functionality (and preferably API) of Socket.io (WebSockets) except using UDP?
In esse
There is a WebRTC module for node.js: https://js-platform.github.io/node-webrtc/
The installation can be really cumbersome (to say the least) but if you succeed you'll be able to make your node.js server act as a WebRTC peer just as browsers do. This way you'd be able to open a Data Channel between a browser and your node.js server.
We have this in use in our research project to evaluate performance characteristics.