Windows 10 Creators Update has been announced by Microsoft for Spring 2017 (March or April). This new feature upgrade will bring also new features like support for 3D. And there are other little improvements under the hood.
One of these things are probably folders for apps in Windows 10 start menu. During Christmas weekend, a new build Windows 10 14997.1001 has been leaked. MSPowerUser reported that this build provides also app folders for start menu.
(Source: MSPowerUser)
The GIF image shown above demonstrates how to use an app folder within start menu. App folders has been long available for Android devices for instance.
