I haven't followed the entire thread, but most systems which shipped with Windows 8 had Secure Boot enabled....
All bioses I have see allow the user to disable secure boot. But these things are at the discretion of whoever is in control of what bios options you are allowed to access....
The reason I would go to a new OS, first of all, would not be based on whether it was free or not. I look at the UI to see if it behaves the way I like and the OS has new capabilities which make it more usable. I rejected Windows 8 except for test machines. Windows 10, just because of the Start button, will be more user friendly than Windows 8. This decision must be left to the individual, and after making themselves aware of all the pros and cons, will make a decision best for them.
The unknown is in the bowels of the OS which would be enhancements most users would never actually see. Hard to make a decision based on something you cannot see.