You know, I just remembered something. Wasn't it mentioned a few months ago that a WoW-style plugin interface for FFXI was being implemented? Because this is the kind of thing that we could get from a third party long before the dev team ever gets to it if they do at all.
You're dreaming. They've mentioned no such thing. Maybe you're thinking of FFXIV, which would more readily support UI mods if the developers wanted to enable it (as my understanding is FFXIV uses XML/LUA for the UI)