I just hacked together a C2 plugin that exposes access to the microphone based on the approach used at webaudiodemos.appspot.com/input/index.html
It works, but it's currently completely unusable in a production environment:
For starters, it only works in the dev build of Google Canary and, even then, you first have to manually configure the Web Audio Input setting via chrome://flags/ (you also have to manually accept access to the microphone when prompted when the page loads). And, because it's running in Canary, it crashes every 30 secs or so.
So, technically possible? Yes. Usable? No.
I'd wait a year or so and see what the adoption of getUserMedia is like then.