We don’t have plans for an iPad pro version at the moment. Yes, it has a beautiful screen, but there’s more to consider, such as how to adapt the UI for touch without compromising the experience.
But the biggest problem is the platform. Apps on iOS sell for unsustainably low prices due to the lack of trials. We cannot port Sketch to the iPad if we have no reasonable expectation of earning back on our investment.
This, I think, is the single biggest problem holding back the iPad. Apple sees the App Store as a success because there are so many apps, and so many downloads. But the Mac has an established ecosystem that allows for sustainable pricing — including upgrade pricing — for professional tools. (Sketch for Mac costs $100.)
I have to agree that Apple has created an environment where many developers will pass on iOS if they have to devote all their resources to one OS or another. The expectation of free or cheap apps and the recoil if anything costs over $2.99 seem to be the biggest pain point, despite the iPad Pro’s (and iPad Air 2’s) power.