Microsoft has finally offered an option to hide the app list in Start Menu in Windows 10 with the new insider build 14942. If you’re an insider in the fast ring, visit Windows Update and install the build and head over to Settings > Personaliztation > Start, and enable ‘Hide App list in start menu‘ and close the settings window and click on the Start button to see the change. Check the below GIF posted by JenMsft to see how it actually looks like.
If you’re using Windows 10 version 1607, you need to wait for some more time for this to be available.
— Jen Gentleman 🌺 (@JenMsft) October 7, 2016