Hard. Very hard.
Michael Foord has a good post about whether Microsoft cares about dynamic languages. Some people [who?] believe that because IronPython/IronRuby don't have full support in Visual Studio 2010 that Microsoft doesn't care about dynamic languages.
I think I can safely say that adding full, high-quality support for IronPython to Visual Studio would require at least a couple of man-years of work. The rabbit hole goes pretty deep when you consider all of the functionality that VS offers, not to mention the difficulty of doing IntelliSense well. I estimate they'd have to at least double the IronPython team to get full support into VS11. IronRuby would require the same commitment.
Also, IronPython and IronRuby have only recently got to the point where I would consider them production-ready. Thus, getting IronRuby or IronPython into VS2010 was never realistic.
Now, if they don't have some support in VS11 (VS2012?), well, that's a different story. At least the IronPython extensions should be pretty mature by then.