I'd put the odds of this feature even being used by most web developers at about 10%. If no other browser supports it, what's the point?
It'd be much better if MS were to just take a page outline (from all the headlines) that were links and make their menu out of that. Or, look at the HTML5 <nav> elements. Then IE9 users might actually see it in use once in a blue moon.
10% of the IE9 users is really a huge absolute number. It's probably larger, too, when you consider it could become applicable to all browsers on Windows 7. If it gains traction, it or something similar might be picked up by OSX or Gnome/KDE.
It's still worth investigating doing it right, instead of letting IE define the standard, and letting it stagnate.
It'd be much better if MS were to just take a page outline (from all the headlines) that were links and make their menu out of that. Or, look at the HTML5 <nav> elements. Then IE9 users might actually see it in use once in a blue moon.