[Deferring comments on the rest for the time being]
Didier Verna <verna(a)inf.enst.fr> writes in xemacs-beta(a)xemacs.org:
...
3/ Importance: 4/5
The presence of the mule subdir appears questionable to me: this
separation is put on the same level as the site-level or distrib-level
split, but it has nothing to do with it.
Mule packages have poison (Mule encoded characters) in the
auto-autoloads files that cause a non-Mule XEmacs to choke and die.
Mule packages are split away in order to allow them to coexist in the
same installation tree used by non-Mule XEmacsen.