Microsoft has paused the development of Windows 10X, its Chrome OS competitor for single-screen and dual-screen devices. Microsoft has now shifted its focus to the Windows 10 Sun Valley Update that will ditch sharp corners for rounded corners, and enable a new Start menu experience. Microsoft also confirmed that Windows 10 X features would be coming to Windows 10 with the Sun Valley and other upcoming features updates. Microsoft may optimize Windows 10 that we use currently for dual screen devices like Surface Neo and Surface Neo.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10x-on-hold-features-coming-to-windows-10-instead/