> The reason why Apple invented FAT binaries is because they were interested
> in maintaining extensive binary compatibility with their old systems.
Actually, Apple inherited fat binaries in Mach-O from NeXT.
NeXT supported fat binaries because NeXTSTEP (and later OpenStep) was available for multiple CPU architectures (68k, x86, SPARC32, PARISC), and they wanted to enable ISVs to ship binary applications that worked on all platforms.
To make that work effectively, they
a) Maintain ABIs, use weak-linking, etc
b) Distribute applications as a bundle
c) Support fat binaries
This is a viable approach, as Apple has recently demonstrated.
But it's a very different model to the usual Linux distribution, which needs none of those things, and relies on the dependency resolution of the packaging system and rigorous testing of API compatibility when building the consistent package set.
I don't think attempting to move Linux towards the NeXT/Apple model is useful, but I also don't see why those that want to can't maintain an out-of-tree patch to make it work.