I am very happy to see portable DLLs arriving.
I would love to be able to re-use more of my code though between WinRT, WinPhone and Silverlight and WPF. (please push as mush APIs as you can into the Portable DLLs)
For example I would like a binary compatible subset of XAML that works in all 4 XAML platforms (and any others that come along).
I have some basic constructs like wizards, message popups, filter editing screens, report viewers etc... and I would like them to be re-useable as DLLs and not just as copy and paste and tweak re-use this is like stepping back 20 years of software development.
You can only use APIs in portable class libraries if they are supported by all the targets you’ve selected. Windows 8.1 and Windows Phone 8.1 now share the same UI technology. So we’re happy to announce that you’ll be able to share the XAML if you’re targeting these two platforms (and moving forward any other platform that will use this UI stack as well).
Thus, I’m marking this item as completed. I’m well aware that this doesn’t exactly address your suggestion but I don’t think it would be technologically feasible to include WPF and Silverlight because both have a similar, but yet distinctively different UI stack.
.NET Framework Team
Mike G commented
Ooops it was supposed to be called "Portable XAML" !!!