In case anyone was wondering Firaxis is definatly listening. In all their recent interviews they have made it a point to emphasize that they are working on an easy to use and powerful external scenario builder. Which is great, that's one of the main features everyone from all walks of the modding community want. Personally I don't think this is a new decision on their part, I'm sure they have been developing this for a while; the Firaxis devs are for the most part Civ4 players (and modders) themselves afterall; I'm sure they knew this was something that needed working on, but it's good to know they are listening enough to confirm this for us.
Personally I'm still very curious about the in game modding shell. But I doubt we'll get much info on this at this time. For one, it's probably still in active development, and isn't at a point yet where they would want to show it off. I'm sure they have a functioning bootstrap, or maybe even an alpha built for it, but I'd expect the aesthetics and more user friendly and intuitive presentation behind it isn't done yet, and that's really what that whole feature is about, so no point in showing us now. Also I'd expect there are some disputes between Take Two and Firaxis itself about the implementation of the system. At least if I try to think about what my point of view would be about this feature from a publisher's perspective it would be drastically different then from a developer's.
Now If World Builder is done, and they have a dedicated programmer working on mod tools, maybe they could put some effort into a simple Unit Editing station. Just something simple that could clone units, swap and import art, and tweak stats, but would utterly break for SDK mods (adding SDK coding support to such a tool wouldn't be worth the effort). Most casual users would be happy with a simple tool that could do such things, and most advanced modders would be off doing something else anyway. But there are alot of casual users that could get a lot of enjoyment out of a simple unit editor. Not that this will happen, and I also don't think it's even remotely important, but this is what I'd be pushing for if I had my hand in the kitchen, and I think it would actually be worth the investment; such a feature would definitely score big points in early reviews at least.