The saddest thing is that a Fallout MMO would seriously be the hardest MMO to screw up, and they would find a way.
Handcraft some towns and plop them down on the edges of a procedurally generated part of the American Midwest. Biomes are grassland, wasteland, irradiated wasteland, hills, rivers, lakes, ruined town(rubble and a couple standing buildings), cavern, and mountains. Throw in the FO4 ability to build a town and make it FFA PVP. Nothing is soulbound because if you die it's pretty easy to loot a half buried filing cabinet for a golf club, beat a couple geckos to death and make leather armor, then beat some guy to death to get his motorcycle helmet and bottlecaps. Basically EVE on land in a Fallout skin.
Instead they'll do some bullshit PVE MMO carebear shit where you join a premade faction (Brotherhood, NCR, Caesar's, Enclave), are friendly with other players, has one shitty PVP zone, and put in ability keys like a traditional MMO because "Some people aren't good at FPS and we didn't want any of our fans to be left out."
So here's hoping they don't try.