The last time Apple had such a system-changing update, it turned Mac OS into OS X in 2001, 18 years into that platform (the same amount of time Apple spent supporting 32-bit apps). I hope it’s at least another 18 years until we learn of the death of 64-bit apps.
Henry’s not the first person to say that was the last major system update, but it misses the PowerPC to Intel transition that started with 10.4 Tiger in 2006. We had Universal Binaries back then that supported both platforms, before the legacy code was removed in 10.6 Snow Leopard, and the Rosetta system to run PowerPC on Intel was removed entirely in 10.7 Lion.
This transition is a longer time coming, but similar in that it’s a wholesale removal of an architecture in lieu of a different one. There are a few theories as to why Apple are doing this, from making the transition to arm easier, to simplifying their code base. Given Apple’s well-publicised QA issues of late, I’d hope the latter would help.
Apple were only on i386 for less than a year with the first generation Intel iMac and MacBook Pro. Part of me wonders had they been able to hold out on moving from PowerPC for another nine months or so, they’d have been able to launch with the Core 2 Duo and avoided all this.