Nope. You can count on there never being an OS X iPad. How can I promise this? Easy. Look at the iPod touch for answers.
As technology has advanced, the iPod touch has had the capability of replacing the iPhone as a phone device. The iPod touch could easily be used as a wifi enabled phone device using VOIP but Apple purposely blocks it from being possible.
WHY???
Because it would take away from iPhone sales. The same would apply to the iPad. The technology is finally there to where the iPad could run OS X. We all know the mobile processors are now more powerful than what laptop processors were out 5 years ago and they are catching up to current processors at exponential increases in performance.
However, If customers could spend $500 for a device that replaces their $799-$1399 laptop, then customers stop purchasing those laptops and sales decline.
Apple is pretty strategic. They market the iPad and iPad Pro as devices that can "do anything" and even want you to think that they are professional, but then they limit them just enough to make customers still want a laptop/desktop to do the heavy lifting for certain tasks.
Don't believe me, just ask anyone with a degree in business if it would be a smart idea for Apple to provide a $500 device that can replace their high end computers.
Their $500 device can replace their high end computers for most people, because most people don't actually need a high end computer. Facebook, email, photos, video, documents...all work fine on a $500 iPad Air 2.
And the iPod Touch can't replace the iPhone even if it had an earpiece, unless you never leave your own home. In fact, iPod Touch already has FaceTime and iMessage...why do people still buy iPhones? Because they need it to work outside of the 20 foot radius of their own house and office. The iPhone IS an iPod Touch, but with a bigger batter and cellular radios/antennas, also all the required FCC licensing to go with it (Also a better display, better cameras and faster chipset which all add up to the increased cost.)
The iPad could run OS X, yes. But it doesn't, because of the UI. Every single Mac app is designed to be used with a keyboard and a mouse cursor. Now replace that with a virtual keyboard and your fingers, and what do you get? A terrible experience, or Windows 10
(Just kidding, it isn't that bad.) If you need evidence, look at your mouse cursor on your mac. Now look at the pixel at the very tip. Compare that to the size of your finger - you finger is about 100 times the size of that pixel.
If you want the full desktop approach - go Surface. Microsoft is trying to build from the top down - start from a desktop OS and try and simplify it to make it finger friendly. Apple is going from the bottom up - start from a touch based OS and add complexity. In this next year I am sure we are going to see some major improvements for the iPad in iOS 10.