Personally, I'd prefer SVG over fonts unless they change how using font icons is done in HTML and CSS.

I was looking for a similar solution recently, and came across Stackicons[0], basically icon fonts with multiple color layers, essentially what Microsoft is proposing.

But there's a huge flaw with the whole approach: you can't have color gradients. Of course you can still emulate gradients by using lots of layers, but it's going to look like crap when you increase the resolution.

[0] http://stackicons.com/