Looking at Five Line Skink (http://s92972807.onlinehome.us/skink.html)
ABC Music frontend, does LilyPond have anything similar? I'm not
thinking on another music notation program now (I think LilyPond should
really do its primary goal - being an engraver), but something similar
to WYSIWYG. IMO RoseGarden, NoteEdit and similar should serve as a
composing tool (when you write a score on your own, you don't really
care how does it look like. You're interested in its internal
structure), but they all have the export to LilyPond function. That's
where the LilyPond GUI should take part. You'd open that .ly file and
prepare the score for publishing.