With everything about the Fallout MMO I was thinking about a Fallout game with multiplayer. Now before you go saying "THAT'S NOT THE POINT OF FALLOUT!" stay back and listen a bit. Now here is my little design, first off the setting.
The setting would be 30 years after the Great War and the Vaults are just starting to open up, in a test of a Vault experiment with Vaults 44, 45, 46, 47 in which they were all supposed to open at the exact same time exactly 1 mile from each other to test how people would compete in the post-apocalyptic world all filled with one group of people talented in a certain area. The place in which these Vaults are located is near the Colombia River, Vault 44 built on the South East corner of the map, Vault 45 on the South West corner, Vault 46 on the North East corner, and Vault 47 on the North West corner (Sorry, I don't live in Oregon). The Chinese launched a few nukes in that area to cause the water to become undrinkable in such a large mass of water and to cripple any people trying to escape east. Some people and ghouls have started trying to make a living ,however that happens to be quite difficult with creatures ready to bite your head off at any minute.
Now time for the actual setup of the server and map. The Colombia river is irradiated heavily with a mountain that has many ways of getting up it and on the other side a flatter area of land. My design has 150 people in 1 server (crazy I know but MAG did it) going either of a few ways, you can be in a Vault of which holds 25 people in 1 group of Vault teams each with their own special abilities (of which I will explain in the gameplay paragraph) and a freelance group (where you can assemble with other freelancers to make your own group and you will get a special ability depending on how your group plays e.g. If you attack mug other groups you get the Raider ability) and you can make it official group by a leader meeting up with people and asking them to be part of his group, and inviting them to join by talking to them directly or sending a courier to them where you go up to a courier (in which you are invincible while talking to and wears off the milisecond you stop talking to him) first you go up to him, then talk to him, select the option of "Recuirt members" and he will teleport to them and ask them to join your group, and you can say either yes or no, and if the recuirts happens to say yes then. Congratulations! You now are part of a group, of which you name and you can either recuirt more members (up to 12 in each group) and such. You can always leave or join a group but the Vaults must have at least 2 members each and always balanced.
Now after reading all of that you must be thinking, "THAT WILL BE TOO OVERPOWERED AND EASY!" well keep reading because there is more (ughhh....I know right?) we will finally cover gameplay. Now you start out with making a character (as with any good Fallout game) with specials, name and all, however they are covered a bit differently you start with 5 in each skill and modifiers with Specials give +2 per point. Strength covers, like always covers Melee, and carrying capacity, at level 1 the weight you can hold is 30 and you go 5 up each Strength point you put in. Perception does skills that FNV takes and the higher your perception, the better you are at finding stuff that people who have less perception wouldn't find. Endurance does hand to hand, and at level 5 you have 100 hit points, +10 hit points per point in endurance, level 1 is 60 hit points. Charisma does Speech and Barter as, always and more Charisma you have is how much other people in the wastes like you and follow you, this is for people who want to be a leader in the group (which are picked by who has the highest charisma before hand in the Vault so prepare to plan with others in the Vault) and you are more likely the higher your charisma to be able to talk a trader into joining your group and the better you are in that statistic the more qualified you are to lead the group. Intelligence does skill points (+.5 per point) 5 intelligence starts at 5, does the same skills as FNV, and the quality of your buildings, the higher the intelligence, the better the quality of the building. Agility does the same skill as FNV and the higher your agility the faster you are, good for people who like to shoot guns. Luck does the likelyhood of whether you'll meet a person who wants to give you some free food to a group of NPC raiders who have the same amount of health as you attack you and crit chance (same as in FNV). Then you pick 1 tag skill that gives 15 to a skill. Now perks are little different then single player Fallout, there is not skill point or hp point upgrade perks like in other games, they are more characterizing perks that give you stuff like cheaper stuff from traders to more accurate with rifles. Now the special ablities that I told you about in paragraph 2, and here they are. Vault 44, with its vast medical staff and standard courses has the ability of stimpacks being more effective and they are able to heal limbs, however they never really gave you much in the way of teaching you how to fire a gun effectively so they get a -5% in damage (since there is no damage increasing perks its not possible to do so). Vault 45, as big on survival as they are on breathing studied the greatest survival techniques from studying the Indians to hearing incredible survival accounts on the holotape they can decrease the bad effects of food and increase the good effects, however they never really gave covered the trading part, so traders don't show ALL of their inventory (at random). Vault 46, where being queen/king of the beauty pagent is as important as living itself, these people know how to talk and charm and they use it all the time, they get a 10% discount from traders and a higher chance of recuirting people, however they aren't someone you'd want to build a house, their houses and other buildings get a -10% decrease in health. Vault 47, guns, guns, guns, some people say they were taught to shoot before they learned to walk, if that's the case then these people learned to shoot in the womb, they get a 10% bonus to accuracy with all weapons that fire something, however focusing on guns all the time can make you really take ammo for granted, when you buy or find ammo you find -5% of it. Freelancers get no bonuses or penalties. Now at the start you create a character,then you join a group if more than needed or more than 2 people are on 1 vault you can't go to that vault since it is "full", then goes the vote of who's the leader, 3 people who have the highest charisma (if more than 3 people have the same charisma the people who are chosen are picked at random if no one votes for them, then people vote for whose going to be the leader, then afterwards you have 3 minutes to plan, and then after all that happens, then its time to set out (as a freelancer you are sent to a bar in the wasteland to converse with other freelancers). If you die you get transported back to the vault where you can do things according to what the vault's theme is for 5 minutes, however standard things like watching the wasteland, listening to music, etc. After that you are transported to your group, if your groups in danger, than you are asked if you REALLY want to go then if you say no you are still in the vault and you are next to the computer that decides whether you want to go back or not and when they are out of danger you are automatically transported back to your group. When you set out to leave or respawning you go to a inventory screen with equipment all with advantages/disadvantages better equipment is out in the wastes. When you are in the wastes your main goal is survival. Time doesn't stop when you go to your pip-boy, your starting items are automatically assigned to hotkeys and can be switched back. Time doesn't stop when you go to a trader,you can't vats, you can't hurt your teammates. You can also build a village in similar style to that of Wasteland Settler like in the Fallout 3/FNV mod. Hunger, sleep, dehydration, sleep, and everything else is essiential to life you have to get or you die. You can branch off but if your leader wants you back he can call you on his "walkie talkie" to call you back and he can set a time of which you have to explore because he needs you back there, the leader can be impeached with a 3/4 vote but then you have to go through the process of voting again without that guy being able to attend that election. The leader has a lot of pressure on him to do right or get impeached (such as mangement of food, trading, sharing supplies etc.)
Now that's done, maybe you can give me your thoughts on and tell me if YOU think if this could work, or give me some more ideas for this, be nice.