Windows Insiders are already enjoying taste of Fluent design in updated Native Windows 10 apps on Fall Creators update preview builds. But as Microsoft reveals in its official Fluent design demo video these changes are part of Fluent Design Wave 1.
So, it seems Fluent Design will come to Windows 10 and native apps in waves. While insiders have access to Wave 1 design via native apps, Microsoft is already working on Wave 2 of Fluent Design. As per the official video, below are the focal points of Wave 2 of Fluent design.
Microsoft has also presented some examples of next wave thinking of Fluent design in the demo video around 42 minutes.