Facebook integration and a redesigned App Store will be part of the iOS 6 (codenamed "Sundance") lineup of changes, amidst previously reported updates like the release of a Siri .apk, Siri voice functions on iPad, and a proprietary, in-house maps application with 3D mapping features.
Twitter will still be part of the new OS and TechCrunch reports that the company will be chatting more about the "continued partnership" (presumably integration into OS Mountain Lion). Nonetheless, the fact that tons of apps currently use Facebook for new sign-ups and authentication marks the importance of Facebook integration in the upcoming Sundance update. The integration is rumored to include "a system-wide sign-in that would allow iOS users to share content from any apps on Facebook without further identification", TechCrunch elaborates.
According to unnamed sources quoted by in 9to5Mac's article, Apple's three major digital stores, iTunes, the App Store, and the iBookstore, are said to face major design overhauls that will see improved interactivity across purchases and to a big extent, an increased social aspect to the experience (i.e., Facebook integration).
Of course, all eyes are not only on the software side of things - the next-gen iPhone is said to showcase a 4.0-inch, longer touch screen, finally deviating from its usual 3.5-inch offerings. The alleged next-gen iPhone and the iPad mini is said to be arriving in September, but bear in mind, these are rumors until WWDC kickstarts officially.