Even if you sort of scale up the panoramas and such, all the assets like icons and such would be super low res. It would never work. I could imagine that in future you could write an app that runs both on Windows Phone and Windows 8 (provide high-res assets and they'll get scaled down when compiled for the phone or something), but existing apps? No way.

I wouldn't be suprised if Windows Phone 8 and its development framework are being specifically designed to work with the whole jupiter/immersive thing though. Maybe he's onto something, but just off by one major version.