Since no one here apparently cares to answer your question, i thought I'd share my experience with HTPC running Win8.1 and tested Win10 with Kodi 14-15~16.
In short, i wouldn't bother until the Kodi team add support for Cortana, as you would need a shortcut mapper for Cortana to even begin to work properly. Also, performance wise, Win8.1 and Kodi are WAAAY better than Win10, general snappiness seems lacking in 10. I actually have 3 HTPC, one high end (i7 12GB, SSD), one HP SFF Core Duo 2, 4GB velocirator and an old MSI laptop, all running Win8.1 and Kodi 15.2, only the laptop has abit of shudder when playing a 25GB direct blu-ray rip mkv, all the others work flawlessly. I tested the laptop and the i7 with Win10, didn't like the feel and overhead that seems to need alot of work to get down to what a HTPC should be running.
Hope that gives you some insight, I'd recommend staying with 8.1 atleast for a while longer.