You may want to have a look at Lanes, that offers inter-state data transfer precisely for the purpose of communication between separate threads each running an independant Lua state.
Lanes is awesome work. However, this is an example of something that is at a higher level than what I was thinking. For example (and as far as I could tell from looking at Lanes), it uses its own message passing functions. We have a desire to stick with nanomsg (or similar), in order to achieve network transparency. This will lead to other issues (endianness, byte alignment), of course.
I'll take another look at Lanes, however. It is an interesting project.
