In his iOS 9 wishes article, Federico gives his thoughts on a possible iPad multitasking mode:
Either Apple is saving a full-blown multitasking mode for an even larger iPad model, or they’re going to announce the new feature at WWDC as a limited mode for the current iPad Air 2 generation. In the second case, new landscape multitasking would allow you to dock a second app to either side of the screen to view information while you’re doing something else. You would be able to scroll and tap in the second app, but any further interaction (showing the keyboard, a camera view, picking a photo, etc.) would require the full app experience, out of the multitasking UI.
I think Federico is on point. A two-app on screen mode should only be available on iPad Air 2 and beyond. This theoretical mode will need the RAM and high-end performance to work well.
It should also be limited in functionality. Two full-fledged apps side by side on an iPad is a recipe for pain. Specific, limited functionality on the second app is key. Think Today Widget taken to the next level.