With their license, they have a huge amount of flexibility and are able to significantly customize the designs from ARM, letting them optimize in ways that Intel and AMD just wouldn’t allow.
An opportunity RISC-V will offer to anyone with a billion dollars lying around.
ARM, being a mature, and customizable RISC arch really should be able to chomp into x86 market share.
x86 market share is 99.999% driven by published software. Microsoft already tried expanding Windows, and being Microsoft, made half a dozen of the worst decisions simultaneously. Linux dorks (hi) have the freedom to shift over to whatever, give or take some Wine holdovers. Apple just dictated what would change, because you can do that when you’re a petit monopoly.
What’s really going to threaten x86 are user-mode emulators like box86, fex-emu, and qemu-user. That witchcraft turns Windows/x86 binaries into something like Java: it will run poorly, but it will run. Right now those projects mostly target ARM, obviously. But there’s no reason they have to. Just melting things down to LLVM or Mono would let any native back-end run up-to-date software on esoteric hardware.