First before reading my suggestion i recommend you to read this topic since it shows most problems for some npc factions:
http://fodev.net/forum/index.php?topic=3881.0 . Now as you read it you should understand, that roleplaying a raider or an enclave soldier gets really boring really soon since you are very limited in places you can visit, mines you can go to mine, and even these mines are problematic. If we assume that if player is enclave then he is loner, if he is loner then vc patrols is heavy test for him if he wants to go to only mine where he wont be attacked. Same is with raiders, you can visit only two mines and san francisco mine is very far away, while vc mine is impossible to visit due to raiders hostile vc patrols. My suggestions purpose is to make more or less all npc factions playable, not only vc citizens. So let the introduction begin:
I suggest to separate all factions into classes. So
Military factionsUnity
Brotherhood of steel
Enclave
Religious factionsHubologists
Followers of the apocalypse
Unity
City based factionsVault city
Raiders
Slavery related factionsSlavers guild
Vortis Slavers
NCR rangers
New Reno mafiaBishop family
Wrights
Salvatores
Mordinos
All other existing factions follows in the "others" category and reputation doesnt change with player being in any of these factions. Now that we have faction classes i suggest one important suggestion that could solve many problems for RP in npc factions. If you join for example military faction (thus unity, BOS, enclave) then only other military factions vilifies you, all other classes doesnt give a shit. It means that if you are enclave you can go to all towns, and just unity mutants and bos patrols will kill you. Same with being in all other factions :>
Another suggestion is to make relations between factions in different classes. For example we have relation between Raiders - Bishop family - NCR. So if i Join vault city, factions related with raiders also gives me negative reputation with them just at lower percentage. So if with raiders i am vilified (-2000 reputation), with bishop family i will be hated (-1000) and with NCR i will have antipathy (-300) reputation. But only the first faction of this reputation attacks me on sight, if i fix my reputation with other they treat me well. Other faction relations i suggest.
Brotherhood of steel - (all towns that bos have offices in Den, SF, NCR)
Enclave - Salvatores
Vault city - Redding - All caravans/FLC
Unity - BH mutants/BH ghouls - Necropolis ghouls/Gecko ghouls
Raiders - Bishop family - NCR
Slavers - Vortis Slavers - Vault city
NCR rangers - NCR
Mordinos - Slavers/Redding
Salvatores - Enclave
Bishop family - Raiders
So what do you think of my suggestion. Maybe you have some useful improvements on it? Express your opinion by voting and commenting :>