RPMMO Fallout 4 with mods allowed. Just my opinion. If anyone can take on the RPMMO market they can.
How? All of the TES series and Fallout 3 are single player. Bethesda, or more specifically the TES team, has no MMO experience. Bethesda makes great single player RPGs, and that is one of the reasons why I love Bethesda games.
TES and Fallout series should stay away from any form of multiplayer, whether it by a MMO or co-op, or whatever.