Elmofongo: "What is DRM-Free Online Multiplayer?"
Online multiplayer where the game lets you join the game/server without any authentication, possibly even without an account.
So as far as I can tell, DRM-free online multiplayer could be done... but I personally don't care for it because in online play the DRM (=requires authentication and it is linked to your specific copy of the game) actually brings benefits to me, the player, in the form of effective banning of evildoers who try to destroy the fun for other players. If such people are banned permanently, then they can't rejoin either by merely creating a new account, using the same game. So in essence, your specific copy of the game is banned from the online multiplayer.
Same cannot be said for single-player, I can't think of ways how DRM can benefit me there. Also, by its very nature online multiplayer is a form of game that is mostly out of my control, ie. it is no fun if there are no other people willing to play it too. So I consider it as the form of game that will die in time anyway, when all other players migrate to other (multiplayer) games.
That's also the reason why I am less likely to use money on multiplayer-only games.