But Swift is an actual example of something with no legacy to worry about. Instead of being Objective C++2015, it's an entirely new language. And, more importantly, Apple can give guidance that people have to follow. As Swift matures, regresses, and has the bugs worked out of it, and library support is fully developed, Apple can arbitrarily identify a point at which Objective C just has to die, and the developers (if they want to develop applications for the App Store, which is 99% of them), will just have to do so.
The nice thing about Windows XP, is that by and large, a Windows XP user could use Windows 7 with next to zero training. Or, in fact, zero training.
This is why the first version of Windows 8 pissed so many people off - removing the Start Button all of a sudden made the Operating System unusable to a huge portion of the Windows user base.
I understand they've brought back the start button.