Anyone who subscribes to the XeTeX or LuaTeX mailing lists will have seen a lot of posts from me over the past couple of weeks, pursuing various aspects of multi-directional typesetting. That might prompt some questions, not least what has raised this interest!
I got a bug report for siunitx a little while ago about interaction with the bidi package. That pushed me to look at something I’ve been wondering about for a while: what we need to do in the LaTeX3 codebase to allow for multiple directions (particularly right-to-left, which as bidi shows should be usable directly in LaTeX). It’s turned out that good documentation on the various primitives available is not so easy to come by, and that there is a lot to get your head around. Luckily, I’ve had some very useful feedback from a range of people, including John Plaice (one of the authors of Omega). It also turns out that not everything is quite settled in engine support for multiple directions, so asking questions is pretty important.