It's their own code. And there's no texture streaming engine to worry about. And they can take as long as they need to get it right.
Microsoft isn't going to give them free control. It's not IG's IP. The PC port is probably going to come out right before Season 3 as a promotional tool (I can't see KI coming to PC with no more content coming), and if it doesn't work before then it's going to cause a lot of problems because 8-9 characters in 10 months plus the PC version is going to cause strain.