Speculations have been over the top in suggesting that Bethesda is attempting to add a multiplayer online mode in Fallout 4. If this is to happen, then it will contradict the nature of the Fallout franchise.
However, the idea is not impossible at all. Looking at the Elder Scrolls series, Bethesda launched Elder Scrolls Online earlier this year to please MMORPG gamers worldwide. For the game developer not to disrupt Fallout 4’s gameplay, they could just be producing Fallout 4 Online too.
In the gaming industry, this is not something new. Rockstar did something similar with GTA 5 by introducing GTA Online. Bioware too offered an Online mode in Mass Effect 4 and Dragon Age 3.
So if Bethesda is to follow the trend, they should at least turn the multiplayer mode into a separate offering. After all, gamers don’t like breaking tradition and also being forced into something different.
With that being said, there is a big chance that the long wait for Fallout 4 is due to Fallout Online. While that sounds likely, it is still best to take it with a pinch of salt since the above is merely based on speculation.