IMO, there has been consistent misunderstanding about the iPad Pro since it was first rumored. There are real "professionals" who have committed to Apple's ecosystem. They may use the iPad, but they really have wanted something like the iPad Pro.
Regarding iOS vs OS X: I used a Tablet PC before the iPad was released. MS consistently promoted the benefit of having access to the same software applications in different environments. The problem with that strategy was that developers had no incentive to work on tablet optimization. Even MS failed to optimize Office for tablet PCs.
The other thing to keep in mind is that Wacom was one of the major causes of the high cost of tablet PCs. Another was the convertible tablet design, which is patented. In fact, Gateway at one point developed a tablet PC that specifically avoided infringing on IP associated with both Wacom and the convertible tablet design. MS has had to take over tablet PC production, because they can basically subsidize it and increase adoption over and above what OEMs were able to do.
Finally, relying on x86 CPUs limits benefits in power management. It's worth considering that MS ran into a lot of problems by reducing the official Vista system requirements at the request of Intel to accommodate the early Atom CPU. In a lot of ways, Surface RT was an attempt to catch up on the ARM CPU front and/or to put pressure on Intel to deliver on improved power efficiency, and that it got scrapped. Basically, MS no longer has the option of pursuing Apple's tablet strategy. And they recognize that, which is why they fully support iOS.
The main thing people want from an iPad Pro is full compatibility with existing software environments — Adobe software, MS Office, Final Cut, Logic, etc. I think that independent app developers, like the makers of Procreate, who are trying to work their way up, will offer iPad Pro versions of apps at low cost. But the established players will expect to be compensated. Software also has changed since the early tablet PC days, and subscription models have provided a new source of revenue. That was the real significance of having reps from both Adobe and MS at the presentation.
The iPad Pro is not intended to be a widely popular product. For instance, I think most casual users would find it to be too heavy. The point is that it addresses the needs of people who work in film and music production, graphic design, visual arts, etc. E.g., a video production company that is shelling out $5,000 to $10,000 per Mac Pro system will have no problem adding an iPad Pro for every employee, as long as they are assured of full project compatibility. In contrast, MS has positioned the Surface Pro more as a corporate enterprise product.
IMO, the real threat is to Wacom, because they're being positioned out. Both the iPad Pro and Surface Pro shore up their respective ecosystems. But neither of them probably will have a big impact on the degree to which professionals switch between Apple and MS work environments.