Comment #5 on issue 2458 by [email protected]: Remove small gaps between lyric syllables
http://code.google.com/p/lilypond/issues/detail?id=2458
Which is the point. For R2L languages, you can't "phase out" a hyphen/gap gradually. It either must be _clearly_ there (in which case you sing syllables left to right, while the syllables themselves are spelled right to left), or it must be clearly absent, in which case the whole word is written right to left, not just each individual syllable.
I don't have actual experience with notational practise in those languages. For non-native singers, it is not uncommon to have a transliteration in Latin letters as well as the original text. I think I remember that for purely Hebrew lyrics, people sometimes mirror the whole music to make it match the text direction. That would be a different problem then.
