This could be a problematic change.  It changes the way :with-subject
works.  I've added changes to allow the subject style to be choose as
a radio list with customize.  The reason is that LaTeX becomes unhappy
if it is not a supported value.  If #+OPTIONS subject:t the default is
used.  If #+OPTIONS subject:my-crazy-string it tries that and most
likely hell will break loose.

Viktor, you're usage of ox-koma-letter.el is quite different from mine
in that you rely (heavily?) on LCO files.  If you could test this and
see what you think of it it would be great.  On my system it doesn't
break anything vital but I might have missed something.  

I have probably overlooked some important case in which case I can try
to fix the patch or drop it.

–Rasmus

-- 
El Rey ha muerto. ¡Larga vida al Rey!