Though I think Silverlight was the natural extension of WPF, which in turn was supposed to be Microsoft's next generation Windows user interface toolkit. WPF/E (E is for everywhere) turned into Silverlight and then interest turned to parity between WPF and Silverlight. For whatever reason (maybe the success of touch interfaces and iPhone/iPad/Android) Microsoft decided to leave behind both WPF and Silverlight and focus instead on HTML5 and maybe optionally salvaging the XAML notion in Windows 8. But you can be sure, it won't be WPF. It'll be something else entirely (WinRT).
And a note about Windows Phone 7 ... true story:
I went to my local Walmart super center the other day. They have a mobile phone store inside. They looked at me funny when I asked if they sell a WP7 phone the other day. The answer is no. I was at my local super mall yesterday where they have three phone stores: Verizon, Sprint, AT&T, and Radio Shack (hey, they sell phones too!). None of them had a WP7 in their store. The Verizon store said they could order one for me, but that they don't carry them in store. When I asked when the manager said because they bounce back. When I asked what he meant by bounce back he said when they sold them customer would be them back and return them for a non WP7 phone.