FYI, I have proceeded with this change.  A bug fix to the kernel was
necessary to make ld.elf_so load when linked with a non-0 VMA on
platforms other than MIPS; however, with that in place, I can now link
and run ld.elf_so with other VMAs; e.g. on my Alpha I have it linked
at 0x100000 right now:

/usr/libexec/ld.elf_so is initialized, mapbase=0x160010000, relocbase=0x15ff10000

As I said before, this change temporarily breaks hppa and x86_64
support in ld.elf_so.  Changes to fix both should be minor, but I
can't do any testing on those platforms.