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Hi, original author here.

Yes, I'm talking about Apple Macs, specifically. I am not aware of any other Apple product line that has transitioned from any one processor architecture to another different one while maintaining any form of software compatibility; are you?

Non-computers don't matter. Nobody cares if a laser printer has the same CPU as the previous generation of laser printer, so long as it still prints and there's a driver. Nobody cares if a new iPod has a different CPU, because iPods didn't run apps.

The iOS line has never made a CPU transition, so there's nothing to write about. It's ARM as it's always been. 32-bit to 64-bit is no big deal; I did a FOSDEM talk on this theme a fortnight ago: https://news.ycombinator.com/item?id=22265615

Only Apple's Mac made a journey like this, so there's nothing else to talk about. The Apple IIGS had a different CPU but was backwards-compatible; no transition involved.

It ends around 2008 because by then Apple was making 64-bit dual-core x86 machines with 64-bit UEFI and they still are. That was their last transition so far. There's nothing more to say.

The 32-bit to 64-bit ARM transition was a huge deal. It was made somewhat seamless to end users because both copies of the entire system stack could be included for a few releases, but it was at least as big a deal as the 32-to-64-bit x86 transition. Moreover, it came with the Secure Enclave, which totally changed the security model for iOS devices.

T2 Macs essentially also moved to the iOS Secure Boot model. There is still an UEFI firmware but it lives in the coprocessor now, and it doesn't do as much as it used to. Many of the things used to run in the UEFI firmware now run in the T2.

You could make the argument that they've made at least a partial transition since the 2008 64 bit UEFI with the whole T2 ARM co-processor thing.

Mac software the way the original author is talking about it is still basically running like 64-bit Intel Mac software, though, right? Catalina is a transition of sorts in that it's dropping all 32-bit compatibility, so that could be a footnote, but I think that's about it -- until-slash-if Macs make the oft-rumored transition to Apple-designed ARM CPUs.