One of the ways we already know that beefy ARM processors can work well (and with better power efficiency than Intel CPUs) for heavier workloads/at higher scale than mobile or embedded devices is that it's already being done in the server space. Is scaling ARM processors up for the desktop radically different? (If so, I'd love to learn a bit about how )

The problem that remains for anyone who wants to sell PCs with something other than x86 is that desktop users want their apps, and for Windows users those apps are distributed as x86 binaries, and users aren't in control of that (especially for unmaintained or legacy software). Software publishers won't build or optimize for a new architecture if they suspect it's just going to be a flash in the pan, and this creates a chicken-and-egg problem.

But Apple can just declare that their new architecture is the only option for you if you're buying a new Mac, and a ton of their users will come with them no matter what. App publishers will just deal with it, knowing that they have to play along if they want their application to have a first-class experience on Mac. This is a huge deal, and not a position any particular PC manufacturer could hope to be in!

I'm sure Apple has done lots of technically impressive stuff that I'm not even competent to really appreciate in order to make this architecture change happen. But other vendors are more capable of technically impressive stuff than they are of forcing adoption for enough users to reach critical mass to get people who sell/distribute proprietary software to come along with them.