[Reason077]

> "Maybe the norm will be 'fat binaries' like in the PowerPC->Intel transition period"

Multi-arch "fat binaries" have been the norm much more recently than that. For a long time, typical macOS binaries supported both 32-bit and 64-bit x86.

Likewise, fat binaries are used to support the various different ARM variants on iOS devices (armv7, arm64, etc).

[Someone]

The first fat binaries on the Mac were 68k-PowerPC.

That time one could also patch 68k OS calls with PPC code and vice versa. Depending on your viewpoint, making that possible, where the 68k OS calls had about 10 different calling conventions (the ABI of some of the callbacks seemed to be chosen by what registers the arguments happened to be in in the first implementation), that was either a can of worms or a brilliant hack.