Fluent Design was definitely one of the biggest announcements for developers at BUILD 2017. We have already seen a Microsoft apps and few other apps on the store getting the Fluent Design. At a session at Build 2017 Microsoft also shared the upcoming Windows 10 Start Screen with Fluent Design demo along with other apps. Have a look at it:
You will see the hovering effect when you move curser on the apps or apps list. If you tap anywhere on the start you get a kind of Luminescence that light emanates. And if you do have a long press for a context menu or stuff like that there is another interaction designed in it.
Microsoft would be planning to release this and more of the fluid Design elements inside the Windows 10 ecosystem in the upcoming Windows Insider Builds.