I'll be frank, this is my post out of a Facebook discussion on the same topic.
This is how I would envision a perfect 3D Fallout MMORPG (not talking about isometric).
Disclamer (one I should have added from the start): This is definitely not a "can someone do this for me" or "we need an MMO for every single game in existence" post. This is more about how I think Beth could make a Fallout Online work, if they ever decided to try.
One way or another, I believe that an MMO should precede all the other games in the series, as not to mess up the future lore, create opportunity for numerous easter eggs (how about giving a plausible explanation for the idiocracy with Jet, explain (or, better yet, imply explanation) numerous questionable moments in the lore, also would not overtake the single-player games the same way WoW overtook the Warcraft strategies.
Players start the game randomly in several different opened vaults or private basement bunkers. The vaults, are under-stocked experiment vaults and cannot sustain habitation, requiring scavenging. Same for the private bunkers.
Hardcore Needs and Scavenging
Have a strict realistic needs system. One that would be reliant on hunter-gatherer approach, scavenging, as well as cooking/crafting.
Basebuilding and Scavenging
Have a base-building mechanic, that would be heavily reliant on materials, and would have a brahmin-like delivery mechanic for those materials from the place of scavenging to the location of construction (using proto-brahmin or reprogrammed robots). Have construction be a prolonged process, that requires involvement from several players, maybe even in several shifts. Also, have an alternative of being able to reinforce existing ruins, or build bases that interface with them.
Have vaults, that would serve as repositories of unique loot and devices, and would open every month or two. Have crafting system, with crafting designs being one of the things players can trade & share.
Crafting would be vital for the game. To create a new crafting recipy of a complex enough object (not spears or bats), you need to disassemble an existing item at a workbench (destroying it and restoring it to crafting materials) and pass a repair/science check in the process, to retain the knowledge of how the item works. This means that when a scavenger player finds a lazer rifle, he has a choice to try and figure it out, at the cost of risking to destroy it, or to continue using and maintaining it with repair, as is. This works for everything. Scavenging specific locations can also help find ready-made recipes.
Monsters and Non-Player Factions, PVE
In terms of monsters and factions. There are no supermutans. Nada. None. Not at the release of the MMO. If the game locations have government FEV labs, the player has a chance to run into centaurs or similarly twisted FEV-monstrosities. Deathclaws are a thing for later as well. Metros, ruined buildings, basements and sewers are home to proto-feral ghouls - crazed, already begining to decay, suffering from visible malnoris Main PvE enemies are robots, giant insects, manged animals (dogs, no mutated mammals yet), proto-raiders (crazed, irradiated survivalists and, potentially, crazed inhabitants of a particularly bad experiment vault or two), american army deserters (occasionally power armored), proto Chinese Remnants (undergoing first stages of ghoulification).
Location & Factions
The location is a large plain, with three or so non-descript enough ruined cities, neighbourhoods, military bases, mountains ranges and bodies of water. Servers have limited number of players, to keep it from becoming too overcrowded. There should be several NPC settlements - several opened vaults, some where new players are spawned, some NPC exclusive, a base of american military, who are also trying to survive and are dangerously approaching shoot-on-site ideology, and aim to recover as much military tech as possible before heading west to respond to a randeveaux signal from one of the major bunkers, and some others.
Trade is done entirely through barter, pre-caps. Objects have an invisible value, and it is up to the players to figure it out.
Skills and Character Development
Skill-wise, the characters have a characteristics, skills and perks, with perks having both skill and event pre-requirements. Encumbrance is limited to about how much a human can carry on him/herself, and can be increased by increasing strength (not significantly, though, I'd say a base 30, +10 for each strength point, where a medium armor weight at about 20, and an unmodded Chinese Assault Rifle is a 9), and much more with additional gear, which can be found or crafted (bags, rucksacks, pouches, clothing).
Health is tied to Endurance and NOT to level. Leveling gives access to skillpoints and perks. Characteristics can be increased with Intense Training perk, or with in-game events. Finiteness of resources should be a mechanic, where a cleared out mall remains mostly cleared out, requiring further scavenging or crafting, to provide alternatives. There, hope you had a nice read. I'd love to play this.
Gear is placed in "slots" on the character body, and can be worn over normal clothes. This will give additional customization options to the player, allowing the characters to look truly unique, as well as giving them additional crafting options and game mechanics. For example, crafting radios (like those seen on some clothing in F3 and NV) for several different players, could allow them to share the enemy spotting skill of the most Perceptive player in the team, or equipping a gas mask to reduce rad exposure. Some outfits can be crafted into gear. For example, combat armor can be stripped into chest protection only, Chinese Stealth Armor, with high enough Science/Repair, can be made into a stealth harness, etc.
Power Armor DOES require Power Armor Training, but functions as it did in F4 in terms of most mechanics, except for energy. An intact pre-war power armor does not require recharging, and can function indefinitely. A wrecked power armor can be repaired, but will require fusion batteries from that point onwards. Killing an enemy in power armor wrecks it, requiring repairs. Transporting intact or wrecked power armor requires the use of the same system as resource transportation (use of proto-brahmin or lifter-robots).