Well, you wouldn't gain anything from player Multiplayer over the net, really. Or at least, not without some *significant* changes.
With the current game, the only way it would work would be by adding "co-op". Having different players each control only one character in the party.
In multiplayer : The problem is that since one player has to make the choices to advance the story, it would probably be the guy who created the game, in which case everyone else is simply a puppet who follows him around. Not very fun, may as well play alone.
So it leaves real-life, the way Co-Op is (usually) meant to be played. The only thing is, if you want to play Dragon Age in co-op, the only thing you need to do is pass the controller along. Separate the characters, decide who plays what, then pass the controller when you're done choosing the actions you want to do.
It won't be the most "clean" co-op ever, but I'm not exactly what else you could do.
(The only "real" multiplayer mode I could see working would be if they completely forgot about the SP Storyline and gave players the ability to make their own campaigns and run them as a D&D game. Keep the engine and mechanics made for DA, but let players create+run (as a DM) their own storylines.)