Avalon does UI rendering and interaction, and makes use of DirectX for compositing the UI elements (to the screen). It doesn't replace it. And DirectX won't exactly be replaced, some bigger changes and renaming it to WGF, as far as I know.
Is the name change needed?
There is so much computer jargon as is, is my point and when I need a customer to download DirectX... I do not want to mean WGF and confuse them.
Please rethink renaming products that end-users will need to get. (or think on it some more)