Teddy Svoronos on changes to Keynote for iOS 9:

When using Split View, only the “main” app can use features like the microphone, camera, and, most relevant to this post, video out. This means that if you’re using Keynote as your main app while Airplaying or using a dongle to project your iPad onto an external screen, only the Keynote presentation will be visible to your audience. This means you’re free to keep OmniOutliner (pictured), Notes, or any other Split View-enabled app on the side of your screen while presenting. As someone who prefers to have my full outline available to me rather than slide-specific Presenter Notes, this is huge.

That does sound like a welcome improvement indeed. A month in, it’s clear that the biggest advantage of iOS 9 for iPad is the increased cooperation between apps. The updated iWork suite is a good example of this.