I actually don't need OS X on the Ipad Pro, I have a Mac for that. Plus I have Astropad and may be considering a off brand Cintiq Graphics tablet for future use, even though I still like my IPP. I agree, I would like some changes to IOS, such as the better filing system. I don't like each App storing the data and I would like an Explorer or Finder like system where you can decide where to store files and access them. It would be nice to be able to use some of the Mac Software on the Ipad Pro, so as an artist I could see the advantages of using certain programs like Photoshop, Painter. I'm only a hobbyist though and in my opinion coming from an artist perspective, I think Procreate is an incredible Drawing/Painting app and more than does enough for my needs. I have so many other art apps that I've only slightly tried or played around with, but I always come back to Procreate to do my work. I guess I'm just more comfortable with it.
I think when you are talking adding OS X to Ipad Pro, the price would be even more expensive than it already is. I see it being more expensive like the Windows alternatives. I also think it will make changes to the Ipad Pro, which I didn't like when trying to use the Surface Pros myself. Requiring more hardware and making it thicker and heavier. Most people complain about the size of the IPP right now as it is. I find the IPP size not too overwhelming and thin, not to mention I don't miss the fan sounds and Heat of the surface pros I had. I have none of those issues with the IPP.