It's a bit of both. It basically boils down to it being an invasive change to core kernel code that doesn't have demonstrable benefit to users, and is specific to one platform. If we can point at a specific application and say "look, this speeds up 300% with AMX" then that might help convince people, but there would definitely be quite some political discussion, not in the least because what Apple did is a violation of the architecture.
I'm hoping we can at least push through a prctl to turn on TSO mode for x86 emulation. I think that one will be simple enough and have enough benefits to convince people.