I don't make a fuss about it but I think that those that do have somewhat of a point...
 

Thanks.
 

Yes, the fewer the better.

In file "ucd.dat", ucd stands for Unicode Character Database. The content of ucd.dat
is a derivative of file UnicodeData.txt published by the Unicode Consortium that is produces by a utility
program that can be found in MKCL's contrib/unicode directory. File ucd.dat once loaded provides the basic
attributes of each Unicode character, like uppercase, lowercase, alpha or digit... 

File ucd.dat was inherited by MKCL from ECL 9.6.2 when MKCL was forked from it.  Its existence as a
separate external file is basically a bad idea (wrong point in the memory versus time design space).
ECL recognized this lately and moved away from it in ECL 12.7.1. Therefore I consider the existence
of ucd.dat as a legacy bug that needs to be fixed and I will include that fix in MKCL 1.1.2.

That fix will have the nice property of making sure that mkcl_boot() will no longer blow up if
it cannot access MKCL's loadable modules directory as it does now on ucd.dat.
Module loading may still require setting MKCL_LIBDIR in some configurations but at least
failure on #'load (or #'require) will not happen during the boot process and could then be
handled through usual condition handling in user code.

As to "how could one go about removing it?",  well it is the usual Read The Source Code
(or Use The Source, Luke :-) and have fun watching all the arbitrary, undocumented
magic numbers embedded in there...  It is basically a pain, but if you want to share that
pain I'll be glad to accommodate you.

Cheers,

Jean-Claude