+ John Resig commentary http://ejohn.org/blog/the-browser-operating-system/

Even though this was done by MSR, there still probably is an implementation. Chris Grier (one of the co-authors) previously worked on OP, a similarly heavily secured browser. OP has an implementation and works (if the performance is pretty bad)

The main benefit is that the IE (or Firefox et al) team can take some of the ideas present and apply to an actual browser with more stringent performance/usability concerns.

I think it's in Microsoft's best interests to build a browser at this level.

You just can't get the performance you need for some applications through the proxy of a browser. Sometimes you just need to touch the metal.

It's interesting to note that Google's Native Client has that same goal.