Apple doesn't have the same control of the app ecosystem on macOS that they do on iOS so they'ed need to maintain some compatibility system like they've done for their previous architecture migrations
They have to convince everyone else to as well though. There will need to be a transition period powered by emulation for third parties, similar to Rosetta from the last time they switched architectures.
They’d have had a very hard time making the PowerPC -> Intel transition without Rosetta, but I’m not sure they’re in the same position now. How many apps on the average 12” MacBook are no longer maintained or have significant asm in them? I’d guess very few. Start with the MacBook and, over time, as Ax chips become faster and more software gets an ARM64 port, transition the whole line. (Not saying I’d bet on this scenario happening, but it doesn’t seem impossible like making the move to Intel without Rosetta would have been.)
One of the important things about the Rosetta transition was that the x86 processors were DRASTICALLY faster than the G4s, especially in mobile. The difference wasn't as big on the G5 processors, but if you had an Apple laptop even after running through Rosetta the speed difference was noticeable.
If they were to switch processors and it was only (say) 10% faster, the hit from the transition layer may make it a hard sell.
Apple has been knocking it out of the park with the A-series processors though, maybe they could make a big enough difference that it would work out again.
There is another important difference: there was no GPU back then (and QuickDraw was not very suited to GPUs. OSX changed that).
Applications where CPU time was mostly drawing on screen (e.g. text editors) worked a lot better than those where most CPU time was in app code. Today the GPU and graphics code is an even larger amount of the processing.
So for a lot of apps it will not be a big problem if the emulation is a bit slow.
