Why? What benefit does a TCP loopback connection provide over the Unix
domain socket (which is generally faster on most OS'es)?
Just a data point: I have lots of special-purpose accounts on my
desktop system, for example when building package XYZ I might create a
specific "xyz" user and group to do the build work, own the resulting
files, etc. So it's very common for me to su over to one of these
accounts and run things like emacs or application-specific GUI tools
as that special user. I use "xhost +localhost" to let these other
accounts display on my desktop; but I basically never have the need
for connections to port 6000 from off-machine anymore (I use ssh for
that instead).
[I realize xauth, or changing permissions on the unix socket, could
probably solve this as well. But the localhost method is really,
really easy :-]