Edward850: Doom 64 never had multiplayer and very much isn't designed for it, so it's rather moot to include that in your question.
pvresovl: no it isn't moot because the question itself doesn't deal with bringing original features, furthermore the classic doom didn't have a lobby to begin with, that was done by third party software
what a stupid thing to be pedantic about
EDIT: and before you come with a haha moment, don't you dare compare the process of waiting other players to join a game in the network with a list of rooms that is obtained online, outside of the old IPX protocol that was used back then
I appreciate what you're saying but Doom 64 is uniquely incapable of any sort of co-op. The level design implemented a sort of brute force workaround to provide "room over room" in it's pseudo-3D maps. Namely, walking over certain sectors activated unique scripting that forcibly "shoved" levels in areas outside the player's view. So, a section that was formerly the bottom floor is, off screen, suddenly "shoved up" (and retextured) to become the upper floor "above" it. As you might imagine, this makes co-op completely impossible, as there would be situations where one player was on the "bottom floor" and one was on the "top" and the scripting can't do both at once.
Now, multiplayer combat is another story. That's doable, but there are no such maps designed for the game. They'd have to do them from scratch, and frankly, at that point it's better to just make more maps for the Doom 1/2 engine.