But, couldn't we test the UI as well? I mean, you can't have awsome engine with stupid UI. Well, you can, but, it would suck.
I am sure that this engine will make its way to Windows Phone 7 and possibly XBOX, so each of those and the PC Browsers will need its own UI. That will mean One Engine (component-ized hopefully) and different UI's for the 3 Screens strategy Microsoft are