You’re talking about mobile here, and I get why—it’s a majority of their computer sales—but most of these arguments don’t apply in the case of the Mac Pro. A Xeon and an Intel mobile processor are different-enough chipsets that there isn’t much motherboard silicon that can be reused between them. (They could maybe reuse the chipset design from the iMac Pro, but Apple kept saying that was a “transitional” design—which I read as “an evolutionary dead-end stop-gap product that we aren’t basing our future design thinking off of.”)
Likewise, I do agree that Apple is likely switching to ARM for mobile—but are there any ARM cores on anyone’s product roadmaps that could power a Mac Pro, or even an iMac? Nah.
I do agree with the greater point: Intel probably do have an exclusivity agreement with Apple right now, and so Apple sticking with them right now isn’t evidence of anything in particular.
But to me, it looks like a natural shift for Apple, in the near future, to adopt a hybrid strategy: if they can switch to ARM entirely for their highest-volume segment (laptops et al), then they’ll no longer need the benefits of having Intel as a locked-in high-volume chip supplier, and will thus free to choose anyone they like for the much-lower-volume segment (desktops/workstations) on a per-machine basis. That might be Intel, or AMD, at any given time. They won’t get such great deals from Intel, but in exchange they can play Intel and AMD off one-another, now that they’re in healthy competition again.
Intel is probably just as aware of what Apple has on its roadmap as Apple is aware of what’s on Intel’s roadmap, so I would expect, if anything, that they’re scrounging desperately around for a mobile architecture that’ll be competitive-enough with the nascent A13 to stave off that collapse of a partnership.