Ryan has launched the FatELF project page where he talks about how with this file format it would be possible to make a universal Linux installation DVD that could automatically handle both x86 and x86_64 systems (or even PowerPC, MIPS, and others too), support for shipping a single shared library, support for kernel drivers targeting different architectures in a single file, and there's a whole range of other possibilities using FatELF.
What Ryan has achieved so far with FatELF is the file format specification along with documentation and then patches to the Linux kernel, file, binutils, and gdb. The patches still to be written are for module-init-tools, glibc, and elfutils. Support for non-Linux platforms right now is just one of the goals.
Ryan has also constructed a proof-of-concept virtual machine that demonstrates FatELF.