Here's the screenshot leak, showing what will pop up over the foreground app when you press a volume control in Windows Phone 8.1:
From the source article:
We have been tipped with a screenshot, which is apparently from a device running Windows Phone 8.1. It has the on-screen touch home, back and search buttons (which is confirmed as coming with Windows Phone 8.1) and then it has volume controls on the top which looks similar to what we have seen getting leaked in China and was confirmed by our sources to be real.
Some news articles are reporting that this panel swipes down from the top of the screen - though I suspect that this is simply an extension of the current Windows Phone pop-up volume control panel. The layout looks very believable too.
Two volume controls are probably enough - Android has up to four independent sliders (depending on which device, OS and skin you're talking about!) and can sometimes get a little confusing. One control for telephony and notifications and one for everything else, is fine with me. Just don't ask me to listen to any Eminem....(!)
PS. See also, from last year, Rafe's summary of Windows Phone 8.1 rumours so far.