gphoto2-devel-2.2.0-2.1 == gphoto2-devel-2.2.0-2.1

Are you installing 32/64bit versions in parallel or why do you need to have the
same package installed twice?

(I am upstream, and may fix something there.)

Yes, installing both 32 and 64 bit versions, for multiarch development.

So, a potential solution would be to install pkg-config files in
/usr/{lib,lib64}/pkgconfig, and change gphoto2-port-config to
just call 'pkg-config --libs gphoto2-port' (or whatever).

We have been shipping pkg-config files in '${libdir}/pkgconfig' for quite some time.

I don't yet see how having two gphoto2-config scripts calling pkg-config would
solve problem of conflicting files - or how a single gphoto2-config script could
properly distinguish between lib and lib64.

However, we could replace the -config scripts by

#/bin/sh
echo "foo-config is deprecated." >&2
echo "Use pkg-config --blah instead." >&2
exit 1

and thus avoid the problem.

The idea is that *in* gphoto2-config, instead of (warning: paraphrased):

 --libs)
       echo "-L /usr/lib"

you have

  --libs)
       pkg-config --libs gphoto2

When you develop for i386 on x86_64, you would set the personality first to
i386; this would make pkg-config pull the 'right' (i386) pkgconfig file, even
though it's the same command line each time.

See curl-config or libart2-config for some examples.

Have you actually checked that pkg-config works as intended on a
i386-personalized x86_64 system? From looking at the pkg-config source code, I
can't see how that should work.

Anyway, regarding the -config scripts... I propose Fedora ships the kind of
-config scripts which work for Fedora, or not ship them at all.

I cannot ship them in upstream, as upstream must support $prefix != "/usr", and
having gphoto2-config set PKG_CONFIG_PATH to ${libdir}/pkgconfig at libgphoto2
compile time would result in different gphoto2-config scripts for the 32bit and
64bit versions, which was the thing you wanted to avoid in the first place.

Ok, I fixed it downstream in a pretty standard way, so that I modified the
gphoto-config and gphoto-config-port scripts to use pkg-config to get libs and
cflags. Since the scripts are then identical on multiarch, the multilib conflict
is now history.

gphoto2-2.3.1-3.fc6 has been pushed for fc6, which should resolve this issue.  If these problems are still present in this version, then please make note of it in this bug report.