A tipster, who claims to have played with an advanced build of Windows Phone 8.1 GDR2 claims following as some of the changes,
Sorting of Settings finally comes to Windows Phone and it will be alphabetically with an option to reach to settings you want just like the apps list.
Mobile data toggle will be finally present in Action center as one of the options
Cortana will go to more regions but still will be in Alpha.
The GDR2 dev preview has been marked for October by our sources, but don’ get surprised if it happens sooner than that. Last, we caught a much more advanced Windows Phone 8.1 version at WP Bench. The version number in question is 8.15.12375.0, which marks a big jump in the version number over 8.10.14157.200, the version, which comes with the update to Windows Phone 8.1 update1.
The tipster hasn’t shared any screenshot or any other evidence with us, but we will keep you updated in case we came to know more.