Sorry, OS X is not coming to iPad Pro. They've already discovered that the iOS 9 iPad keyboard resizes to a larger resolution screen. The keyboard has more keys to be more like a MacBook keyboard, and that's about it. Look it up.
100% sure here that iPad pro is getting iOS 9. Kind of unfortunate actually. I feel like iPad Pro would really need OS X to really shine, really be a unique product. iPad Pro is shaping up to be a blown up iPad already, nothing special. Hopefully Apple really has a trick up their sleeve with iOS to really let the iPad Pro actually have something going for it, because right now, I don't see iPad Pro taking off.
I know OS X is NOT touch-friendly, but I feel that they could make it so. No, it wouldn't need to be something drastic like Windows 8, but just add certain gestures to close things, redesign a few things that involve drop down menus, etc, etc.