@amigadave
I think KimmoK was asking about something like Apple's universal binaries.
They all use different loaders, but if the newer systems recognize and execute Amiga hunk executables under emulation/JIT, then you could in theory write a startup module that detects the host environment and then dyanimcally reloads itself as a native app on MorphOS, OS4, etc.
The downside would be the size of the binary, which would need to accomodate images for all the various platforms. If you start thinking about separating the loader from the binary images, then your back to just having separate executables. The only upside would be a single installation image that needn't change from platform to platform.
Someone else (Piru?) may know if a single ELF binary could be constructed to run on MorphoOS, OS4, and AROS.
Anything's possible, of course, but it may not be practical.