I wouldn't buy one but I think the market is there for Apple. They need to compete with the Surface. But I'm not sure if putting OS X on the Pro would be the right move. Just add a keyboard and mouse to iOS and I think it would work great. Apple already added new keyboard functions in iOS 9 so I think Apple may be hinting towards that.
Noo - I think it does need full OS X on it, in order for me to return my surface pro and buy it.
Why would I care about a bigger iPad?
The whole appeal would be in being able to run Logic Pro/music notation software, atleast for me.
iOS significantly lacks in that department when compared to desktop apps.
If it doesn't offer full OS X support, then why release it at all? The surface line will always beat it..