Wow this mod looks great! Can't wait to play it!!
Just wondering, for that ability for New Vegas to only have 4 cities (+1 if they somehow get an extra), is that a modified version of Venice's Serenissima or a custom lua code?
Also, have you thought of putting the Shi faction in the mod as well? :3
The New Vegas ability is definitely going to have to use custom lua, since I know Venice's trait is built on a couple of XML components along the lines of <CantBuildSettlersOrAnnexCities> and that also somehow ties into the player getting a Great Merchant when they otherwise would get a Settler, and Vegas doesn't have a Great Merchant replacement, so I dunno. And I haven't played enough of Fallout 2 to decide if the Shi are relevant/powerful/large/"civ-vy" enough to be a civ, let alone design one.
I was actually thinking of making some Fallout mods. I brainstormed some ideas for it and compiled them into
this. Take whatever ideas you like.
Wow, this is pretty good stuff! I like that you included religion preferences with a few canon religions. That gives me an idea to make a little Fallout Religions mod to release alongside the first pack, but I dunno exactly what religions would be included. A few to compliment the planned civs, but maybe some notable others from other factions? And then there's the issue of names for some of them. I'm thinking, as a starting point:
Followers Of The Apocalypse, preferred by the NCR;
Son Of Mars,
preferred by the Legion;
Codex, preferred by the Brotherhood; and the
Children Of The Cathedral and
Children Of Atom for fun and to round it out.
Additionally, you've pretty much cemented the idea some have suggested of doing a Joshua Graham-led Zion civ, perhaps for a Pack 4 (or 5, who knows). Here's a very rough design I came up with, based primarily upon your design:
Zion (Joshua Graham)
Start Bias: Hills
Capital: Zion
UA:
Way of The Canaanite
Gun-based units receive a 10%

Combat Bonus vs other Gun units, increased to 20% within 2 tiles of a city that follows your Religion. Receive double

Faith from Natural Wonders.
UU:
Dead Horse Warrior (Replaces Warrior)
Unique Warrior for Zion. Receives +1 Sight while in Hills, and receives a boost of XP if it is the first unit to discover a Natural Wonder. Additionally, is affected by the Way of The Canaanite trait and receives a bonus vs Melee and Gun units.
UB:
Sacred Cave (Replaces Shrine)
In addition to the normal effect of the Shrine, provides +1

Faith for every Mountain or Natural Wonder within 3 tiles of the city. Costs no

gold maintainence.