Anyways, our sources mention that GDR1 will be mostly about fixing bugs and improving performance of Windows Phone 8.1. GDR2 may bring some new features and even broader hardware support, but not big changes UI wise.
Though, we can confirm that “interactive tiles”, which were leaked in some videos posted by Microsoft research center (Pulled later) are seriously being considered as a part of new Metro UI design-language. Windows Phone 9 is the next Windows Phone iteration supposed to bring major changes UI wise and interactive tiles may be a part of those changes. You can watch leaked interactive tiles videos here or by going to our YouTube channel.