Good point, but remember Apple license the ARM architecture from ARM (the company), and they probably aren't allowed to deliberately ship partially-compliant ARM hardware.
Apple is much bigger than arm and could easily change the rules.
They may be smaller, but they have IP Apple needs now. Apple just can't do whatever it wants to just because it's big.
Every now and then I see a new comparison of the Swift/ObjC dispatch assembly. Now imagine — that could be a single opcode. Or the dispatch table could get pinned to a particular cache. Or it could be other micro-optimizations that they are in a unique position to exploit with full control of the language, compiler and chip.
I have no idea how feasible these things might be or how much of a gain it would create, but they can look through their corpus of LLVM-IR and identify hot-spots where a new opcode would speed everything up by some margin.