In a disappointing announcement tonight Brian Chen (a New York Times technology reporter) has announced that the split screen features believed to be the flagship change in iOS 8 will not be unveiled at the WWDC
I've been told that the split-screen feature for iOS 8 isn't ready yet and won't be shown at WWDC. Still a work in progress.
— Brian X. Chen (@bxchen) May 29, 2014
Apple are apparently still working on the feature, and are not quite ready to bring this into the spotlight just yet.
It’s not yet clear if this feature will be available to all devices. As more information becomes available, I will update this post.