Perhaps better titled "the Mac's long journey", since it's only about one Apple platform and not really about processors. And even then it seems to end around 2006.
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.
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.