Both Bethesda Game Studios and id Software have been trying to hide this and keep it as a surprise, but I have discovered the truth. Fallout 4 and Doom 4 will be released together in the same package. They have even gone so far as drop the '4' in Doom 4 to aid in their deception. We are meant to be able to cross between the two universes. The portal that will take you from the Fallout Universe to the Doom Universe will be found in Vault 666. So you will get your wish.