Windows 10 S, the Microsoft Store-only version of Windows, is going away, but not really.
Currently, Windows 10 S is a unique edition of Windows 10. It’s based on Windows 10 Pro; Windows 10 Pro has various facilities that enable system administrators to restrict which software can be run, and Windows 10 S is essentially a preconfigured version of those facilities. In addition to locking out arbitrary downloaded programs, it also prevents the use of certain built-in Windows features such as the command-line, PowerShell, and Windows Subsystem for Linux.
For those who can’t abide by the constraints that S imposes, you can upgrade 10 S to the full 10 Pro. This upgrade is a one-shot deal: there’s no way of re-enabling the S limitations after upgrading to Pro. It’s also a paid upgrade: while Microsoft offered it as a free upgrade for a limited time for its Surface Laptop, the regular price is $49.
Nothing much actually seems to be changing; it just turns Windows 10 S from a version into a mode. Pretty much a distinction without a difference. My biggest issue here is that you can’t go from regular Windows 10 back to Windows 10 S if you ever had a reason to do so (e.g. if Windows were ever to be usable with just Metro apps in the future and you want the additional security Windows 10 S provides). Seems like an odd restriction.