One that could easily be turned back into the look of the previous version, with the Windows Classic theme. Because it was bitmap-based, it also enabled a lot of interesting theming possibilities. Not so with Win10.
At least with Windows 10 they seem to be dedicated to sticking with something for a while as they plan to continuously update the same OS for a long while.
It won't be "the same OS" for long if they "continuously update" it... that and the forced updates mean that MS can effectively completely change the UI any time they want, and there's very little users most users can/will do about it. Even the fact that it will still called "Windows 10" means it gets a lot harder to refer to what exactly the OS is. It's a new era of learned helplessness and corporate control.
Perhaps a date based naming scheme like CentOS might help as updates are universal outside the corporate sector?
https://wiki.centos.org/FAQ/General#head-dcca41e9a3d5ac4c6d9...