I think there's a lot of confusion of terminology here, which I guess is partly Microsoft's fault for overloading "metro" to mean a bunch of different things. Are we talking about the Windows Phone design language, or the more vaguely defined Microsoft-wide design philosophy, or the Windows 8 immersive windowing model, or the WinRT application model, or the set of new shell features in Windows 8 (live tiles, contracts/charm flows, etc.), or what?
From the rumors it sounds like the main thing they are de-emphasizing for "classic" PC form factors in future Windows is the immersive windowing model, in favor of fitting the new features (including Start / tiles) into the stacked-window desktop model instead. I personally wouldn't characterize that as "abandoning metro" but just reducing the focus on (or decoupling) one aspect of it.
I think Chris Anderson's answers at 9:09 - 11:34 in this video -> http://channel9.msdn.com/Events/Build/2014/9-007 are probably salient:
T: So Charice wants to know: Does XAML in Windows 8.1 code work in Windows 7 WPF desktop application or do we need customization?
A: That's a fabulous question! WinRT XAML is not accessible to desktop applications in Windows 8.1, so you have to write the UI again.
H: Especially not downlevel to Windows 7. We got some parts of this question earlier. WinRT is built on other improvements in Windows as well, that don't exist in Windows 7. It's hard to decouple some of the optimizations of some things like our composition, and aspects that just aren't there in Windows 7.
T: Absolutely. And this kind of goes back to when I jokingly said something like - one XAML. Right - One Microsoft, OneDrive, One XAML. Do you foresee sometime in the future where there actually could be one XAML that runs in different runtimes, or different contexts, like WinRT, desktop - it's something that would be really interesting.
A: Of course. I think that in Windows 8, we coupled a bunch of decisions together, around app containers, and security models, and store distribution, and programming models, and windowing models, and all of these other things. We put a bunch of these decisions together and we called one side the name of M which cannot be spoken, and the other side we called desktop apps. I think you see already in the keynote, and the work we've been doing, and where we've taken the 8.1 experience and where we're going in future releases, that we're starting to take those decisions and decouple them and make them be independent. So Harry showed a demo that showed you being able to break out of your app container and call full-blown native .net code to access LOB functionality. We saw Terry show a demo where there were some hints at future windowing ideas, that we're looking at decoupling that. And so I don't know if I necessarily say that the XAML we see today is going to suddenly light up in desktop, I'm just not sure how long that distinction between those two experiences is going to remain, and which decisions are going to be where.