Two things (pretty late so don't expect much)
-modern operating system : look at the BeOS, and it was with th 80s tech/paradigm, I'm sure we can have better than that today.
-dropping legacy support doesn't mean you can't write an emulator on your system for legacy stuff, just like Virtual PC, or WINE.
Food for thoughts...
Counter argument: where do you draw the line / how do you define legacy? Is
everything before this point considered legacy? What pieces do you eliminate, what pieces do you depricate, what peices do you allow? Who makes this decision? How much time do you spend on virtualizing those legacy components? What is an acceptable performance tradeoff (Virtual will never be at "full speed", obviously)
As for progress on "groundbreaking OS paradigms",
Microsoft Research is the responsible Redmond party for doing such things. A recent example would be the
Singularity operating system, which is only open to certain tech colleges, but is at least one example of them thinking a bit further outside the box.
Again, this really boils down to a huge problem: you have "computer morons" who will complain when the computer doesn't act like an appliance. You have "computer savvy" folks who complain when they can't immediately figure out how to do the stuff that they generally think they know how to do. You have the "tech weenies" who will complain that it never needed to change. And finally you have the "tech gurus" who will see it and love it.
Why cater to the upper eschelon? Any new OS they create (from Win31 upwards) is going to face opposition from at least two of those over-generalized groups I just lumped together. Does that make their OS bad? Nope, but someone will think so and will shout loudly to anyone and everyone with ears or a browser.
You can't please 100% of the people 100% of the time -- I think, so far, Microsoft has done a great job of pleasing most of the people for the majority of the time. If Linux could say the same, it would be gaining marketshare. Maybe that's why Apple is (incredibly slowly, mind you) starting to pick up a little? Dunno...