I know it’s not officially supported but I gave it a try on a new Windows 10 Pro x64 build.
Windows 10 is supper fast and loads from boot to OS in 3 seconds with a Samsung 850 Pro ssd. I loaded only Cubase Pro 8 x64 with no 3rd party plugins. I created a new project and recorded 20 tracks of drums, with 3 guitar and 1 bass track. I went on to record a few midi tracks with patches from HaIion Sonic. I saved this project and was able to close it and open it multiple times without issue.
The only issue is opening older projects recorded in Cubase Pro 8.0.20 and 7.5. When opening these projects from the same SSD drive a window opens (reading project file) 25 minutes. I waited and the project finally opened 40 minutes later. Hmmm. Maybe it was something in that project causing the issue but It has the same result opening all older projects.
I’m now back to Windows 8.1 pro x64