[aseipp]

ARM literally doesn't allow public instruction set extensions by compliant license holders. Apple is presumably only allowed to do this precisely because they do not sell or otherwise offer their CPUs with any other software, with any other documentation, which hides this implementation detail entirely from all users, and I assume this allowance is worked directly into their specific ARM Architecture License.

Apple themselves designed probably half (or more) of the ARMv8 standard themselves. I assume they are pretty aware of what avenues are available to them in this case.