Paul Thurrot has a number of rumours up about Windows Phone 8.1. Two stand out to me.
Where GDR3 is widely expected to support 5- to 6-inch screens, 8.1 will supposedly support 7- to 10-inch screens as well. This obviously infringes on Windows RT/8.x tablets, so it's not clear what the thinking is there.
So, Windows RT will become even more pointless than it already is.
This I am not happy with. The back button is my main navigational input in both Android and Windows Phone, and I miss it dearly in iOS.
I'm just hoping on performance improvements, still my biggest issue with Windows Phone. I used my HTC 8X for a few hours today, and I was stunned by just how slow everything is compared to Android 4.3. Of course, application quality is another huge issue, but there's little Microsoft can do to convince developers that their Windows Phone applications are more than just side projects done between serious work on Android and iOS.