I think what IlluvatarTheCat is refering to is a number of the items that appear on
this page where the lua language is extended at the core level (take the lua interpreter, add code to the interpreter and recompile).
Unfortunately, we cannot use any of these types of extensions inside WoW. In fact, many of the pure lua extensions cannot be used because many of the components of the Lua language itself have been removed from blizzard's version of lua that is used inside wow (i.e. all os and io libraries are missing).
There are some pure lua extensions that can be used within wow, but care must be taken to test them thoroughly to ensure that they do not call upon some language element that is missing.