I came in this thread to say that Microsoft are implementing WebRTC, but when I double checked it looks like it's more complicated than that. There's an API that they want, and may have gotten into the spec called the Object RTC API, but they aren't currently planning on implementing WebRTC as existing browsers speak it: https://status.modern.ie/webrtcobjectrtcapi
I think the plan is for Microsoft to ship Object RTC API in IE, and then to ship some sort of a polyfill on top of that that lets you talk to WebRTC over Object RTC.