Re: "delivering linear scalability"
Well, "scalable" is not a property of the ARM architecture really, but of a specific implementation. It seems this is 128 cores with a single socket; if it runs 128 times faster than a single core then they can call it "linear scalability". Now admittedly I haven't read anywhere whether you can add 2, 3 or 4 sockets to a server.
For the 4 sockets with x86 CPUs: If four CPUs run faster than one, then it is scalable. If they run 4 times faster than one, then it is linear scalable. I have no idea how fast these four CPUs would be.