photonboy :
It seems likely that Apple will begin to integrate Vulkan as the technology matures to the point of replacing Metal. I see no financial incentive to resist this path. They make money from software sold on THEIR hardware so i don't think it matters how the software gets there.
They certainly
do have an incentive not to use standard technologies. Anyone in the apps business cannot afford to ignore iOS, due to the share of iOS devices and the amount of money typical iDevice users spend on apps (they're less cost-sensitive than typical Android users). Therefore, developers will use whatever technologies Apple supports, whether it's standards-based or not. However, if it's non-standard, then it will serve as a hurdle to supporting other platforms.
Now, I know several people who've had iDevices and switched to Android. I know others who are considering the move (back) to Android. One concern people often have is whether their favorite apps are available on Android. So, if Apple makes it harder for developers to maintain apps for both platforms, it typically works in their favor.
This is a tried & true platform play. Nothing new about it. Microsoft long ago even showed how to tweak it with the "embrace and extend" maneuver, wherein they'd adopt standards and then make them proprietary by adding nonstandard features that would help lock in developers who (sometimes unwittingly) made use of them.
Basically, standards are for losers. Only if you're a minority player could adopting standards work in your favor. Sad, but true.
As soon as you understand this, you'll start seeing examples all over the place. For example, why do you think NVidia pushes CUDA and has crap OpenCL support? Meanwhile, AMD and Intel have supported OpenCL as a way to try to win developers away from NVidia. Just like your point about Apple, NVidia makes money on hardware. But the way they lock people in is through software. The day it'll change is the day NVidia loses dominance in HPC.