Store applications are not the only applications on Windows 10. Closing holes in store applications alone does not close all the holes.

This article is addressing sandboxed applications.

Regular applications, yes, you can pretty much do whatever in userspace in Win/Mac/X11. If you're going to create a new sandbox environment for applications (Windows Store/MacOS store) in today's world, it really needs to be locked down with explicit permissions for each type of I/O access.