Microsoft is monetizing Windows 10. That process started with Windows 8. I am fairly sure they could make further changes to Windows 8.1 to access the same revenue streams as Windows 10.
They could not, however, change the Start Screen in the same way Windows 10 is done. But would they really need to change that since the Windows 8.1 version was their original solution.
I suppose we can speculate all day long. But for the next year, Microsoft is going to have the help of those who chose to stay with the Insiders Program to test future changes. I think many folks understand that Windows 10 is just an extension of Windows 8, but leveraged with a working Start Button and a free give away to get as many users on 10 as possible.
Something which I have not seen mentioned is, if Microsoft succeeds in going to a one OS fits all, there will be an over abundance of software engineers at that company. I would expect possibly 50% of those folks being laid off after Windows 10 is accepted as the primary OS.
As a user which appreciates the power of a Desktop PC, I think Microsoft and I have actually parted ways.... Since my Gaming system is still Blue Screening with Windows 10, it seems Microsoft is not too concerned about the gaming systems.