Apple's Hardware technologies team, headed by Johny Srouji, has been the worst-kept secret in the industry for years, but with the iPhones 6s and iPad Pro, they've become impossible to discount. Not that some aren't trying really, really hard. From Engadget

What Apple has done, then, is create a powerful tablet chip, one with a processor that addresses the ARM instruction set and a graphics component that utilizes PowerVR technology. It's not a leap forward, and it's not out of nowhere; it behaves and performs exactly as a chip with as high a clock rate and as large a power draw as the A9X should do.

Which is like saying "it behaves and performs exactly as a hypercar should do" even when it's not your parents' bull crest on the hood.

As I said in my iPad Pro review, Apple is currently the company designing the most interesting silicon in mobile. Intel hasn't been able to duplicate the success they enjoy with PCs, and Qualcomm and Samsung were caught flat-footed by Apple's custom 64-bit A7 processor and are still finding their way forward.

Since then, Apple's been working on custom graphics as well. From Anandtech's recent breakdown:

it's worth pointing out that while Apple doesn't talk about their chip design and licensing process, it's highly likely that Apple has been doing their own layout/synthesis work for their PowerVR GPUs since at least the A4 and its PowerVR SGX 535, as opposed to using the hard macros from Imagination. This is why Apple is able to come up with GPU configurations that are supported by the PowerVR Rogue architecture, but aren't official configurations offered by Imagination. A8X remains an especially memorable case since we didn't initially know Series6XT could scale to 8 GPU cores until Apple went and did it, but otherwise what we see with any of these recent Apple SoCs is what should be a distinctly Apple GPU layout.

That's what happens when you hire some of the best people in the business and let them run as fast and as far as possible. It's also what happens when you have the luxury of designing specifically for you own needs, carry no cross-platform burden, and don't have to worry about profit and loss at the chipset level.

Which brings me back to Engadget:

According to [Patrick] Moorhead, Intel came close to putting one of its chips inside the iPad Pro. "[The iPad Pro] business is open to both Apple's own ARM-based AX chips and Intel," he explained, "Intel is fighting hard to get that business and I believe almost had [the iPad Pro contract] with the new Skylake-based Core M had it been available earlier."

Given the above, my guess is the closest Intel came to putting Skylake inside the iPad Pro was that blog quote.