This weekend, a version of Windows 10, build 10568, got leaked on the Internet via pirate sites. While it first appeared this build didn't have any new features, it's since been discovered that this version will give users messages if they attempt to stop using some Microsoft apps as their defaults.
Specifically, The Verge notes that the leaked Windows 10 build pushes out a message if a user sets their default web browser to something other than Microsoft Edge. It asks the user to "give Microsoft Edge a shot" and notes some of its features as reasons not to switch. Similar messages show up if a user switches their music app default to something other than Groove Music, or their photo app to Microsoft's own default version.
It's important to note these messages are only showing up in the leaked 10568 build of Windows 10. They are not appearing in the current RTM build (10240) nor in the most recent build that Microsoft released to Windows Insiders for testing (10565). It's possible Microsoft could tweak this new feature before it becomes an official part of Windows 10, or simply do away with it completely based on feedback from users.
Source: The Verge