There was plans for World Builders Guidebook once upon a time, not sure whatever happened to it.
Being worked on, though it may take a while (I have seen the first chapter though, and boy, does it have some detail
This is a book that I am really excited about, especially if it takes into account some of the cool exoplanets discovered over the past decade. It's sobering to remember that when Traveller was originally published the existence of solar systems beyond our own was unproven and our knowledge of what they might be like was entirely theoretical. And yet, now we have identified no fewer than 846 planets beyond our own solar system - some of them very bizarre indeed!
However, I do agree with torus that a tight emphasis on how to use the information generated in your games is desirable.