Given that Oracle are adopting fully ARM hardware for their enterprise cloud services from next year courtesy of Ampere ARM based CPU's, so it's not just a theory any more - HPC via ARM is no longer just a pipe dream. Also, because of that, Apple will struggle with trying to say the architecture prevents expanding to that scale. So, with a little bit of extrapolation it should be fairly safe to say that ARM could quite easily replace a current Xeon W or Xeon Platinum, because that is exactly what is happening for Oracle.
It's not quite true to say that Oracle are "fully adopting ARM hardware". Oracle invested $40m in Ampere, and will be using ARM for some workloads from 2021:

Oracle adds Arm-powered servers with up to 160 cores to its cloud – must be why it sunk millions into Ampere
Plans HPC play with AMD, Intel silicon, too

Ampere’s Arm Data Center Chips Come to Oracle Cloud
Oracle said it will launch bare-metal and VM instances on its cloud early next year.
They also use Intel, AMD and Nvidia in their cloud service offerings, and will be launching new services on the latest products from these vendors, so are not replacing them completely.