The latest draft of the CSS3 writing modules came out recently, and it includes revised specifications for how to handle vertical East Asian CJK text as well as specifications for RTL (right-to-left) text.
Although minimal support for RTL text has been around in recent years, vertical text remains a hurdle, partly because it’s not clear which standards the vendors will agree to. The only browser I know supporting a vertical text spec is Internet Explorer, but it’s layout specification was developed by Microsoft, and it does not appear that it is being adopted as is for CSS 3 (see proposed CSS 3 vertical properties for details). It also looks like a vertical text scheme for SVG is also being deprecated.
Will vertical text be possible across platforms? Only time will tell.