In /usr/share/emacs/site-lisp lot of packages install additional lisp files for emacs. All this extension are loaded "automagically" into emacs and every user can use them. The corresponding directory /usr/lib/xemacs/site-packages for xemacs is nearly empty (just gnuplot install some files). A lot of the extensions for emacs work for xemacs e.g. psvn.el from subversion - but there is no easy way to use this .el files in xemacs.
I agree that there is a lot more that can be done here. Looking at this is on my to do list, but only after I have updated all of xemacs in portage and fixed most of the bugs. I expect it may take a few months to get to it. It would be helpful if you could list the specific packages that you would need to be fixed in this way.
I'm closing this bug because there are no specific actionable items in it. Looking at this issue is still on my todo list, but I don't think the bug should remain open for that. If there are specific packages that should get xemacs support added then please open new bugs for each package.
just for the recorsds: i have checked all packages in my emacs directory, most of them work, just 4 fail to load; strange is subversion list: package name (filename) strange fail: dev-util/subversion-1.4.2 (/usr/share/emacs/site-lisp/70svn-gentoo.el) but /usr/share/emacs/site-lisp/subversion/psvn.el works fail: app-emacs/php-mode-1.1.0 (/usr/share/emacs/site-lisp/50php-mode-gentoo.el) sys-devel/gettext-0.15-r1 (/usr/share/emacs/site-lisp/50po-mode-gentoo.el) app-emacs/nxml-mode-20041004 (/usr/share/emacs/site-lisp/80nxml-mode-gentoo.el) load ok: dev-util/gtk-doc-1.7 (/usr/share/emacs/site-lisp/60gtk-doc-gentoo.el) dev-util/cscope-15.6 (/usr/share/emacs/site-lisp/50xcscope-gentoo.el) dev-lang/erlang-11.2.1 (/usr/share/emacs/site-lisp/50erlang-gentoo.el) sci-visualization/gnuplot-4.0-r1 (/usr/share/emacs/site-lisp/50gnuplot-gentoo.el) app-emacs/haskell-mode-2.1 (/usr/share/emacs/site-lisp/50haskell-mode-gentoo.el) app-emacs/graphviz-dot-mode-0.2 (/usr/share/emacs/site-lisp/50graphviz-dot-mode-gentoo.el) app-emacs/jam-mode-0.1 (/usr/share/emacs/site-lisp/70jam-mode-gentoo.el) app-emacs/python-mode-1.0 (/usr/share/emacs/site-lisp/60python-mode-gentoo.el) app-emacs/sml-mode-4.0 (/usr/share/emacs/site-lisp/50sml-mode-gentoo.el) app-emacs/rst-mode-0.2.9 (/usr/share/emacs/site-lisp/50rst-mode-gentoo.el) app-emacs/ocaml-mode-3.08.1 (/usr/share/emacs/site-lisp/50ocaml-mode-gentoo.el) app-emacs/vhdl-mode-3.33.8 (/usr/share/emacs/site-lisp/50vhdl-mode-gentoo.el) app-emacs/rnc-mode-1.0_beta3 (/usr/share/emacs/site-lisp/50rnc-mode-gentoo.el) app-emacs/cedet-1.0_pre3-r2 (/usr/share/emacs/site-lisp/60cedet-gentoo.el) app-emacs/ruby-mode-1.8.4 (/usr/share/emacs/site-lisp/50ruby-mode-gentoo.el) app-emacs/mmm-mode-0.4.8-r1 (/usr/share/emacs/site-lisp/50mmm-mode-gentoo.el) app-emacs/xrdb-mode-2.31 (/usr/share/emacs/site-lisp/70xrdb-mode-gentoo.el) app-emacs/tuareg-mode-1.46.0 (/usr/share/emacs/site-lisp/50tuareg-mode-gentoo.el) app-emacs/pymacs-0.22-r1 (/usr/share/emacs/site-lisp/50pymacs-gentoo.el) app-emacs/apache-mode-1.1 (/usr/share/emacs/site-lisp/50apache-mode-gentoo.el) app-emacs/crontab-mode-1.18 (/usr/share/emacs/site-lisp/50crontab-mode-gentoo.el) app-emacs/css-mode-0.11 (/usr/share/emacs/site-lisp/50css-mode-gentoo.el) app-emacs/lua-mode-1.26-r1 (/usr/share/emacs/site-lisp/70lua-mode-gentoo.el) app-emacs/inform-mode-1.5.8 (/usr/share/emacs/site-lisp/50inform-mode-gentoo.el) dev-python/docutils-0.4 (/usr/share/emacs/site-lisp/50docutils-0.4-gentoo.el)
Thanks for checking these packages. I've reopened the bug so that this list can be worked on. Note that a number of these packages are available in app-xemacs/* for xemacs.
/usr/{lib,share}/xemacs/site-packages does not correspond to /usr/share/emacs/site-lisp. It is the root of a package hierarchy, like xemacs-packages or mule-packages. If you want to use that hierarchy for random bits of elisp, you can drop them in /usr/share/xemacs/site-packages/lisp/site-lisp/ (the "site-lisp" is arbitrary), but that's rather annoying. Alternatively, you can enable the traditional site-lisp directory with --with-site-lisp=yes. I believe this defaults to /usr/share/xemacs/site-lisp in current beta XEmacsen, and /usr/lib/xemacs/site-lisp for XEmacs 21.4 and older.
For packages missing in xemacs open specific bugs reports if support is wanted for a particular package.