As much as I love Civilization. It doesn't work with Fallout. No, let me re-iterate that. It would the worst Fallout game to exist, even F:PoS would be better in comparison.
1. We don't know ANYTHING about civilian life. Almost everything we know is war-related.
2. Even if you did know SOMETHING about civilian life, it'd be carbon copy of Civ albeit with less everything.
3. There's not enough factions for it. You would have four factions tops. If you made the Brotherhood chapters their own, the only difference would be a few unique units. And adding new factions would be pretty hard.
I think you're taking the idea too literally. If they just copied eveything from one game and replaced some wlements it won't be too great.
1. And we know a lot about the NCR, civilians included, remember Fallout 2. We know a bit about Caesar's Legion. And we know a good deal about the BoS.
2. And again I think you are taking it too literally.
3. Again it isn't civilization, it would have similarities. The maps would be way smaller. Essentially it would be like Civilization Revolution except different. And Firaxis would have to make it, otherwise it would fail.