hi tenuun,
i talked to jean (one of the lead developers) about your request and, sadly, he does not have time to get into this today.
here is what he could say right now:
"""
adding vertical layout is lot of work.
not just a matter of rendering top to bottom.
necessary work goes down to the fonts level.
"""
so, you should be prepared to spend some time on the project!
but if you manage to do it, you will make many people very happy!
i also mailed the person who took charge of the right to left rendering in scribus and asked if he has some time for you.
as said, personally, i cannot help you much with the details, since i have no idea about the text engine, but if you come to the irc channel on freenode, you can ask (simple) questions and possibly get answers.
ciao
a.l.e