FATELF seems uneccesary. Why not just put your 32-bit binaries in one filesystem, and your 64 bit ones in another. Then use unionFS to merge one or the other into your rootfs, depending on which architecture you're on. No need for a big new chunk of potentially insecure and buggy kernel code.
The reason why Apple invented FAT binaries is because they were interested in maintaining extensive binary compatibility with their old systems. Linux has never had this policy. Binaries that worked great on Fedora Core 9 probably won't work on Fedora Core 12, or Ubuntu 9.04, or whatever.
> One might question the wisdom of using Hans Reiser as an example of the
> kernel development process gone wrong