As I said before, in my undeniably arrogant opinion, if any Fallout MMO wants to be a "real boy", it needs to lock things down and make itself friendly to people who actually expect a Fallout experience with a multiplayer flavor.
Personally I'd go all Putin on it and get rid of PvP entirely. PvP in MMOs always struck me as one of the most retarded ways to battle other people online.
Not only most MMOs use the laggy TCP/IP protocol, which is unsuitable for realtime battles in client-server WAN situation, but there's also the gear which can automatically negate skill, not to mention the level differences, and there's always some retarded exploit floating around.
My version of a Fallout Online would use Fallout 1/2 single-player as template, with mostly people completing quests, spruced up with Blizzard's "world phasing" technology. The quests would have to center around more-or-less permanent threats, but some of them would "phase" an area into a changed instance of it, and push you forward in the narrative.
People would be able to team up and trade. The SPECIAL system and its permanence would be dumped and reengineered from the ground up. This is because MMO and SPECIAL are not compatible, and I care a great deal more about having the game work, be fun, and fuse harmoniously into its new form, rather than sticking a square peg into a round hole.
Every two weeks there would be a new development in the wasteland, a change somewhere in the quests and/or NPC dialogue and/or location mechanics. It would be pushed through after observing general flow of players' actions and preferences in the previous few weeks, with careful and yet unafraid pushing forward of the world storyline.
New threats would be introduced, old threats would be eliminated, notable player feats would be noted and integrated into the existing narrative/history, and so on and so forth. Failures would be as important as successes. If people aren't feeling enough peril, I'll give them a massive invasion or a disaster of some sort, and integrate them into lore. Of course, this would require efficient, automated tools.
And a log would be kept of all of this, so that new players could go back and see the history of change in area of their choice. Find out why a village is now named after a player group that staved off an overwhelming invasion for hours before getting wiped. Etc.