If it's time to make another CPU change, why not switch it to one that you control completely? Motorola->PPC->Intel->Apple. It just makes sense that's where they'd ultimately want to go.
Rumors were that from the first days of OS X, there was a skunk works level group at Apple ensuring Darwin compiled on Intel chips with an eye on being able to make the switch. I wouldn't place bets against the same thing being in place with ARM chips especially with Apple's ownership in the chips.
I bought a PPC Mac 9 months after they first made the switch. Most of my software was already native. Within the next year, all of the important software was native.
There's a lot of creative software that didn't survive the ppc switch. Back then the chasm between MacOS and Windows for certain workloads was a mile wide and despite all the software lost, which would never be recompiled, users stayed with it.
With recent changes to the OS, a decade of instability with every update every year, the recent hard deprecation of 32 bit binaries, and now moving to an unproven ISA for those particular workloads - all while Windows and Linux have closed the gap, mostly... the situation is a bit different.
This is not going to be the year of the Linux Desktop. What creative software got left behind during either transition? ARM is not an “unproven ISA”. Both Microsoft and Adobe already have ARM versions because of iPads. Besides, unlike the 68K transition, the amount of assembly code in most applications are small
Both previous switches were fast enough that an emulation layer could get most legacy stuff running at a decent speed, I wouldn’t be surprised if the same went for this one. We did just have the 64-bit apocalypse though.
So you don't have to kill all of the software currently running on your customers' machines.