REMEMBER CITADEL
Banned
I think Horizon 2 will get announced for PC at the Windows 10 event though.
I don't know where Playground stand on that, but Turn 10 have said that they would never just port an existing Forza game to PC. Instead, they would build a new PC game from the ground up. I'm expecting a new PC game-as-a-service Forza series at some point, maybe even announced this year (although I doubt that they would want to overshadow FM6 with such an announcement).
It's also interesting to note that a 2015 release date is not mentioned even once or at least I haven't seen it.