No one has successfully done it.
No one has successfully done it.
You can upgrade with the tool Microsoft sends for Windows versions, which usually provides a fresh key or transforms your existing activation key into a Windows 10 one. After that, you can retrieve the key with any key extractor and perform a clean installation when the Windows 10 ISO becomes available.
The pkeyconfig (a file containing valid products keys) for Windows 10 seems to contain the ones for 8.1 and 8, but I'm not sure if Windows 10 will see them as valid for an edition of Windows 10. We also don't know if the Microsoft activation servers allow these keys to be activated. I suggest that you install Windows 8.1 pro and wait 10 days until Windows 10 is launched. It will be possible to do a clean install.