The OGG container format is currently under consideration https://dev.modern.ie/platform/status/oggcontainer
Supporting Ogg container is necessary in order to use Ogg/Vorbis and Ogg/Opus in the audio tag. All other browsers (besides Apple's) support it already.
Opus is now in preview builds behind a flag. Please see https://blogs.windows.com/msedgedev/2016/04/18/webm-vp9-and-opus-support-in-microsoft-edge/
There is a gotcha though. While Opus, Vorbis and VP9 are planned, Ogg container is so far only under consideration: http://dev.modern.ie/platform/status/oggcontainer/
Which seems to indicate that Ogg/Opus or Ogg/Vorbis in the audio tag won't be possible for now.
Please add Opus support. Now that IE supports it for WebRTC, there is no reason not to support it for the audio tag as well!