Although 1v1 Multiplayer would be cool I would be incredibly surprised if they added it. Its kind of just confusing to even begin to imagine how it would work if it were pvp although co op could work. I THINK with a capital THINK they said they were not going to add multiplayer.
I don't get what's confusing to imagine how it would work?:p
Go into a lobby, select 1 vs 1, perhaps both players get the option to choose how big their playspace is , cause some people might not reach the other if they have less roomscale then the other, or some "get close to each other technique" which might be implemented in later on.
All that's left is just each person controlling one character until the other dies ^=
What would happen if you got knocked out (Not killed) You cant look around because that would make no sense if your character was meant to be knocked out, and you cant just see a black screen because a lot of people will think its crashed and probably tell the dev it crashed, And dont get me started on how the physics would work when they were hit hard enough.