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.
Split-screen multitasking would let iPad users run two apps at the simultaneously, side by side in landscape mode -- a feature that Microsoft often criticizes the iPad for lacking. Sources also claim that the feature is designed to allow for apps to interact with each other. For instance, a user can drag content (text, video, images) from one app to another.
It is reported that the multitasking feature will be limited to the iPad Air at launch, although it is unclear when iPad Mini would get the same feature. Apple is again rushing to release iOS 8, so some other major features might have to wait until 8.1.