With Fallout 76 struggling after the sloppy start I have been thinking of how to do a Post Apocalypse MMORPG. This what I came up with...

Game set in a world where Nanites were created. These nanites need wireless power and signal generators to function. For a time they were a benefit to mankind streamlining manufacturing and health treatments. That is until some hackers access the signal generators and implanted a virus. Billions of people died as the nanites went to attack mode. The Gray Goo nightmare began.

Cities all over the world started melting as the nanites ate at skyscrapers. People and animals dropped dead as the nanites stopped hearts or impaired other life functions. The Rampage of the techno virus was slow as the corrupted data went from system node to system node.

Enough time that some Scientist figured out how to make signal jammers creating safe Zones. This is the starting areas. The safe locations are few and brave souls have to venture out of the safety nets into the corrupted areas transporting goods from one Safe area to another. From time to time the safe areas are attacked by corrupted life forms mutated creatures appearances are both biological and technological. Also called Cyborg mutants they could be dogs with robotic spider legs or rats with knife-like blades along the spine. To mutated human cyborgs, both biologic mutations like multiple arms or eyes to cybernetic mutations like weapons for arms. There a wide range of possibilities of such foes.

The more powerful foes stay away from the safe zone due to the signal jammers interference causes more malfunctions in larger and more powerful foes. (In-game reason for area level zoning).

There is a light of hope in this techno waste. The very nanites that destroyed the world can be controlled via devices adventurers have on there person. As you level up your body absorbs more nanites, with a control unit you can override the signal from the corrupted nodes. Much like the Signal Jammers a personal control unit prevents the signal to corrupt the nanites in the player character body. With the control unit a player can manipulate the nanites they absorb to guide mutations. (leveling up and class selection system).

Landscape can be post-apocalypse to Alien landscape where the machines have taken complete control.

Possible surprise storyline. The hacking that triggered the end of the world was not from a human but from an AI and now the cities of the world are massive supercomputer data centers.

Weapons can range from melee swords and blunt weapons. Range via traditional guns, or even energy based weapons generating focused EMP blasts to disrupt the nanite infested life.

Players can make camps but need to set up a portable signal jammer to make an area safe. If a player doesn't recharge the generator powering the camp the signal jammer dies and the area is reclaimed by the corrupted nanites and all traces of the camp disappears being dismantled.