Hangul characters upright or sideways in vertical flow?

Hello,

I'm sorry to ask you guys about vertical flow knowing it's not of much interests, but it'd be great if someone can help me to resolve an issue we have: whether Hangul characters should be rendered upright, or rotated sideways in vertical flow?

I was thinking it should be rendered upright, and I believe MS Word does so, but there's a proposal to rotate them sideways:
http://lists.w3.org/Archives/Public/www-style/2011Oct/0104.html

I understand Korean doesn't use vertical flow these days. But this could also affect EPUB, where you may want to create old documents in EPUB or HTML format for e-book purposes. I'm also not sure Korean never use vertical flow, or still rarely use.

Your opinions are greatly appreciated in advance.


Regards,
Koji