Wow! Quite a thread you started here, Jody, by asking one simple question.
My thoughts is that MS will concentrate on 10 now with no further additions except security updates for 8.x. 8.1 was a fix of what 8 should have been. Just the option of booting to the desktop and using the Apps Screen would have made all the difference in the world, although I don't think that it would have gained the notoriety of 7 of which "traditionalists" seem to want to hold on to. It's surely time to move on to the next OS in what I consider to be a compromise.
Windows 10 is really nothing but 8.1 with a new screen door on the front of it, meaning the return of the Start Menu. It's not the traditional menu, but rather a mini combination version of the Apps Screen and Start Screen.
The other big difference is that the Store apps run along side of Win32 apps on the desktop with somewhat better snapping rather than their own screen forcing one to use the desktop as paulsalter stated. Upon closing apps one is left on the desktop instead of returning to the Start Screen no matter if one uses the Start Menu or Start Screen. The option to boot to the Start Screen is greyed out for now, but if and when it is in option I'm hoping it returns to the Start Screen. Really not a big deal for me to push the WinKey to return to it for now. I also auto hide the Taskbar, so for it to be just a screen to me.
For the record, the Apps Screen is what really replaces the Start Menu, not the Start Screen. A company can configure to boot to the desktop and use the Apps Screen as an alternative to the Start Menu. This can all be configured via Group Policy. App links can be easily columned there for employees to find with ease. It can also be configured to use the Start Screen in the same way.
I am in very much agreement with what asvent is trying to convey. 8.1 is very much usable in the enterprise environment. MS's number one priority is to write OSs directed at that environment. That's what made them the successful corporation that they are.
MS will pursue and eventually develop one OS to run across multiple devices. A number of good reasons for this. Familiarity for employees and the commoners is one. Hand them any device and it will be familiar. Buy or develop an app once and run it across multiple devices. Ease of development for apps also. Side loading of customized apps fit for a particular business type across multiple devices all configured via group policy. This will simply make IT more efficient for a lower cost.
The statement that users are leaving Windows for other platforms is simply not true. A little research will show this. Maybe true for mobile devices but not for the desktop. Users will simply try the "next OS". The "year of linux" will never happen. Apple can sell all the over-priced fashion devices they want and Google can sell all of the cheap devices they want to, but in the end MS will come out way ahead of the game with one OS and apps across multiple devices. Slowly, but surely I think they will succeed. It all makes too much sense to me anyway.