Centennial (read, non-UWP) apps can be published to the Windows Store and don't get any sandboxing beyond registry virtualization by default. Microsoft lives and dies by backwards compatibility, they're not going to kill off Win32 - they may very well push for the Windows Store to be the primary source for applications with traditional installers being blocked by default though.
Unless those non-UWP apps are browsers that use non-Microsoft rendering or javascript engines.
I don't think that's a dealbreaker, especially when they'll let people trade from 10S to 10Pro for free. But it's a pretty big caveat that got added very quietly.
