It might be a doddle to put it into IE and IIS, but they can't take HTTP out of IE because then it wouldn't talk to the vast majority HTTP servers that are not IIS. Taking HTTP out of IIS would be nearly as pointless. First, it would give non-IIS users one more reason to not use it. Secondly, it would give existing IIS users a whole new set of headaches.
Now, being Microsoft, they will probably not take HTTP out of IIS (or IE) but add all sorts of bells and whistles to this new protocol to do things they either can't do or can't be bothered doing via HTTP. Non-IE users on IIS sites will be requested to use IE for the "full-experience", which they probably won't do en-masse. But Microsoft will have a huge PR battle because it will be obvious they're using their IE-near-monopoly to try to co-opt HTTP...
Wade.
P.S. Firewalls will need to know how to let it this new protocol through. :-)