Evaluate source compatibility for existing C# WinRT apps

[Scottj1s]

While it's been agreed that C#/WinRT may introduce source-level breaking changes, it's important to at least understand the scope and nature of these breaks, and get ahead of them for customer messaging.

[jkoritzinsky]

The primary one that I know of is casting between interfaces that are not related in metadata. In the old system, a regular cast would dynamically work. In the new system, you need to use the .As<T>() extension method to cast outside of the type hierarchy in metadata.

[jkoritzinsky]

New item that we recently discovered: If you want to hold a weak reference to a WinRT object, you need to use WinRT.WeakReference<T> instead of System.WeakReference or System.WeakReference<T>.

[AdamBraden]

uber tracking issue for breaking changes.