In fact Windows 10 got (as it was originally meant to be rolling release) and still gets major updates (untill next year if I remember correctly), and it is quite likely they do involve also changes in kernel level. "Main engine" of operating system. Alpha stuff is for internal development use only, consumer may subscribe themselves to beta access.Also lots of blah. Windows 10 is not changing any of its underlying main engine. When they do, they do it in alpha for a new iteration of windows.
SC has changed its database with PES and still need Server Meshing. They are absolutely not "new features" but a deep changes of infrastructure.
These points are done in what is called an alpha.
Likewise many Linux distro's use rolling release model, by your definition they are permanent alpha's?