You could as easily call it a setting as an adventure, where some "game is afoot" and detailed to the level customary for published adventures rather than settings.
Speaking of settings, and drifting off topic...
The Gateway sourcebook works on the basis of "here's a political/historical framework plus 3% of the systems, you are free to do as you wish with the rest". D&Ders might think of this as the "Greyhawk" approach, compared to the "Forgotten Realms" approach of "we detail as much as possible to save you the effort".
It would be nice to have the second option for Traveller as well. Some bunch of ten to twenty systems, walled off by politics or astrography to give PCs a reason to stay in them. Detail every system plus the overall politics of the group, their outside enemies, their forces and diplo/intel setup, etc. Then a ref can come along, ask what PCs and game the players want and decide where they fit, plug in some of those generic adventures I was talking about, and have a game with minimum homework. [Once more, some people enjoy the "homework" and that's fine. But some of us aren't too enthralled by it...]
Something like the Old Worlds pocket empire in Crucis Margin could work nicely. All the usual campaign types would fit, in both low and high octane variants. There's everything from safe internal spec trading to fleet engagements against the Kafoe Dominate, via spying on the Katowice Conquest and diplomacy to the other pocket empires. It's just begging for a 50-100 page book.
