If they could make it so that you could dock it and use Windows Desktop/big boy Metro apps, then remove it from the dock and use it as a Windows Phone with metro phone style apps it would be game over.
That would be my device forever.
And I think Microsoft is within striking distance of this right now. Metro has already proven to be VERY scalable, from phones all the way to giant T.V’s that Microsoft has shown off. I’m using WinRT as my main computer (laptop is blown) and it’s already running well on smartphone guts. Not perfect. But well enough that the thought of getting other devices that are not as capable does not make sense. (looking at you iPad/Android tablets _ ps I have an Android phone and like it). If WinRT could make phone calls what’s the point of having a separate device to do that?
If they could nail the transition aspect of what I described there is no reason to say Win 8 + WinPhone is a bad proposition. The pluses FAR outweigh the minuses for any average consumer.
And I’m willing to bet it IS the future and will be the only thing Microsoft can do to save itself in mobile and save Windows in general.