Didn′t they use it to make the game anyway? So, basically it should be finished already, isn′t it?
Not quite.
The Dev's version:
Can access the code of the game to change stuff thats hard coded. In theory, could be used to directly access the source code.
Has third partys tools for modelling/textures. Bethesda is licensed to only have them for their use, they can't distribute them, so they have to be removed.
Probably isn't in an easy to use package (ie, one icon to click and start with a few additional library files.
It probably also isn't streamlined in its operation. It does need to be usable by people with no coding experience
All those things do have to be addressed before it can be released.