There was no opposition to implementing this, but some barriers were identified.
- We know of some bugs in browser support, but that was not seen as a big problem since it won't impact anything else.
- Some languages actually switch between directions these days (Chinese, Japanese, Korean can be horizontal or vertical, and are often vertical in print) (Use language variants ?)
- CSSJanus will need fixing for vertical support. Actually doing this would be trivial and Roan & Trevor will gladly help anyone to do this.
- However before fixing CSSJanus, we need a language -> rotation map, like we have for rtl/ltr directionality. Ideally we would get this information from CLDR (http://unicode.org/cldr/trac/browser/trunk/common/properties/scriptMetadata.txt), but it is not in that so we need to bolt it on top of our language data first. (the Translate/Localization team can be involved)
- Scripts will need rotating. style.top becomes style.left, width > height, $.slideUp > $.slideLeft, etc. hopefully some way to make this at least semi-automatic. (Since we don't have too much centralization of this and significant upstream, this might be problematic)
- Automatic rotating of inline styles for languages that need to switch between rotation. (if we start with the languages that don't switch [ASL] then this would be less of a blocker.