My only Windows 8.1 computer is an Asus Transformer tablet. I updated it to 10 twice, the first time choosing the 'revert' choice that Microsoft gives you for 30 days.
The second time, I had decided "I should give it a second chance" so I did the Update again. After updating, though, I set the tablet aside. A half hour later I noticed it was still glowing (folded down into the keyboard). Power management was not working at all. So I tried to figure out what I needed to do to get Windows 10 to update for power management. Was there a driver update missing?
I couldn't find any driver updates, and tried to force it to switch off, because nothing I could do would power it off. Once I started fighting with it, it blankscreened and would do NOTHING anymore. I had to do an [F9] System Restore, wiping the tablet clean, to put Windows 8.1 back on it.
I'm pretty leery of putting Windows 10 on my Windows 7 desktop machine. I can't find any information that says that Virtual Box works. It will run, but the 'loopback' (wrong term for it?) networking interface doesn't install according to forums I've read, so I would loose my virtual Windows XP that I use to run some Win32 applications that quit working with 32 bit Windows 7. There is a virtual PC system built into Windows 10 Pro, which is what the desktop would upgrade to, and Microsoft implies that it runs any other OS, even Linuxes (NetBSD?), but I've liked Virtual Box and have my VMs all set up and running the way I want. And who knows what else would quit working. I have some Win32 applications that still work in 64 bit Windows 7 that I suspect might not anymore.