We know that iOS 9's split-screen feature is coming to the iPad Air 2, but now according to fresh information coming form 9to5Mac, it seems that the upcoming new iPad mini could be getting the feature, as well.
Developer Hamza Sood found proof in OS X El Capitan in the form a resource file. The file has been from within the upcoming platform's Safari browser and as you can see from the above image, it makes it clear that an iPad mini will get the "half screen" capability.
Furthermore, the developer also found a tool that can simulate different Apple devices to allow devs to test the responsiveness of their websites, as well. Here are some more details:
"The resource file shown above from the upcoming OS X El Capitan’s Safari 9 browser shows support for a split-screen view of Safari on the iPad mini. Additionally, a developer tool in El Capitan for testing the responsiveness of website designs allows developers to simulate an iPad mini 3 (which does not support split-view) running Safari in a split-view mode. With both the testing capabilities and settings image present in the upcoming version of Safari, we believe that the functionality is coming in a future iPad mini update."
Apple is expected to be releasing a new iPad mini on September 9th, so that's when we will know for sure if the smaller iPad is indeed going to get this really useful feature.