I present to you my new module: Android N-ify! It allows you to use several features introduced in Android N on your Lollipop and Marshmallow device!
The module supports the new settings dashboard with subtitles that show you the most important information. Your notification shade will be completely redesigned to match the new look in Android N. This includes the new Quick Settings and header design. Quick Switch (double-tapping the recents button to quickly switch to the previously used app) also got implemented. More features will be supported in upcoming updates.
Have a look at this module in the support thread! There you can also find some additional information about what’s supported, what will be supported in newer versions and what’s impossible to implement.