Every audio stream in the OS should be backed up with an OS-based Mixer control, is my point. We had it in BeOS and now it seems .. its finally possible in Win7 .. but yeah .. these aren't the only OS's around to run Chrome on ..
So if you have 50 tabs open, the OS should expose 50 audio sliders somewhere??? How will you know which one is for which tab? Also, isn't it better to be able to CLOSE that tab rather than letting it continue play audio and just mute it?
If you have one channel in the system audio mixer for every channel that the system is playing then yes: you can just see what channel is active and mute it. Like on any old mixing desk.