> Proprietary programs that are only available in i386 versions.
That does not mean that you need a i386 userspace for them. Multilib works just fine in that case.
> That's not my experience. Quite often, proper distribution-supported packages (i.e., not roll-your-own installations) for i386 shared libraries in x86_64 base installations are missing. I.e., one has a 32bit program, and no vendor-supported package is available with its needed libraries that can be installed.
Not sure what distribution you are referring to but at least on fedora every lib shipped does have a installable i686 counterpart in the repos. So for every libfoo.x86_64 there is libfoo.i686 ...
> And no luck at all on RHEL.
What does that mean? Just install libfoo.i686 (you can do that for every library shipped assuming they are doing the same as fedora which I have no reason to doubt).