I’ve seen a few stories about this lately but seriously people if you think for a second Ballmer saying something is ‘interesting’ means anything, especially that MS will drop the IE rendering engine, forget it, no way in hell MS will adopt Webkit.
Don’t forget parts of it are used in Office as well as a number of other places in the OS (how did they get round the claim that they were getting unfair advantage? Oh yeah, they claimed it was an inseparable part of the OS, and then made it so).
Having special functionality in IE means apps built on top of it work better, give people a better experience and mean they can continue market dominance. If IE worked the same as any other Webkit browser why keep using it?
Not that I don’t think it’s a good idea, they could shrink the development team significantly and focus on other areas.