Android 6.1 Rumored to Include Native Split Screen Support
Google seems to be following Apple's and Microsoft's lead, as the "point" update to Android 6.0 Marshmallow (6.0 -> 6.1) will reportedly allow multi-screen support. Android 6.1 is expected to debut in June 2016.
Companies like LG and Samsung have devised workarounds for Android's lack of split screen mode, but if these rumors are true, it should pave the way for a plethora of developers to make use of the function.
If you don't feel like waiting until June for the official release, the feature is hidden in the Marshmallow 6.0 release and can be unlocked on your device by following these steps. There's no way to resize the windows, and there are a few other quirks, but it should get you by for the time being.
Android 6.1 is also expected to further improve on the granular app permissions framework that was an important yet relatively unheralded feature of Marshmallow. Other than that, Android 6.1 won't be much different than the current version, based on the information we have on hand.
Also, there's a chance that Google won't follow its tradition of naming subsequent versions of Android after a dessert in alphabetical order. CEO Sundar Pichai said in an interview in India that they may open up naming of a future release to an online poll. Let's just hope Google has learned a lesson from previous online polling mishaps and doesn't allow user-submitted entries.