Killer Instinct is already available on Xbox One, but with the upcoming Season 3, it'll launch on PC as well, but that's only if you have Windows 10.
This was confirmed by the game's creative director, Adam Isgreen, in an interview on Twitch. In addition it was also confirmed that the PC version will launch sometime in March, and will include "an updated Dojo Tutorial", as well as some tweaking in order to "help balance the game to compensate for the new features and mechanics being introduced in Season 3."
Thanks, Reddit.