> They can take the ARM ISA and extend it in any way they want, and they can take ARM cores and adjust them, or design their own-- they have already done all of this (though to a small degree, not enough to be called a "new ISA".)
What is your source for this? As far as I know ARM do not permit modification of the designs they sell or alterations to the architecture. After all allowing such things could lead to the errosion of their business (e.g. by letting apple slowly slide to a non ARM architecture).
"Companies can also obtain an ARM architectural licence for designing their own CPU cores using the ARM instruction sets. These cores must comply fully with the ARM architecture."
Given the lego-like structure of the ARM instruction set (the 32-bit variant), with zillions of extensions (Jazelle, DSP instructions, Neon, Thumb, Thumb-2, various revisions of vector floating point instructions) and explicit support for "coprocessors" (https://en.wikipedia.org/wiki/ARM_architecture#Coprocessors), I suspect (based on common sense and nothing else) that the license allows expanding the instruction set and dropping whole modules.
But as I said elsewhere: concrete proof for that is lacking.