Responsive to the touch
A user interface that flexibly adjusts to the users needs has to be fluent and shape shifting with intention. What makes sense on a desktop environment doesn't necessarily work on a tablet. While the space on a 27" monitor feels almost infinite there is only little room for UI elements on a phone screen. While using Windows on a phone the start menu should cover the full screen to take advantage of the small space. On a desktop the startmenu can be reduced to a pop-up menu that only appears on demand.
Following that philosophy we don't end up with a one-size-fits-all approach, but with precisely tailored experiences for each use case and each device type. So that the operating system feels native and familiar at the same time on whatever device the user chooses.
Our devices become more and more intelligent. But opposed to all technological achievments they lack personality and humanity. The people bar puts front and center what is most important to the user. It makes it easy to quickly share and communicate and helps focus on what we use our devices for the most: Staying in touch with friends, family and team members.