A system-wide dark mode is depicted in the images, offering up an example of what darker backgrounds would look like in Messages, Mail, Contacts, News, and more.
The concept also features split-screen multitasking and picture-in-picture support, bringing the iPad feature to the iPhone when used in landscape mode.
Personally I think an automatic system wide dark mode would be awesome to have. That way we could choose between using the current Night Shift feature or the new potential Dark Mode.
I also believe it could be true that we will get the split-screen feature that the iPad has, also for the larger iPhone. Maybe not for the iPhone Plus though, I believe it's for the rumored 5.8-inch iPhone Pro. Then all Apple's Pro iOS devices will have the same features. Apple Pen support, Smart Connector and split-screen view.