I think, truth be told, that Mass Effect is a good setting for a multiplayer game. Now, hear me out here.
1. There is demand for it.
2. If EA wanted a multiplayer "mode", this would be a better situation than tagging MP onto ME3.
3. If they make it a TPS rather than an FPS, they should be able to also rival MSG's Gears of War games.
4. It's a sci-fi setting with a variety of weaponry.
5. Story? In my multiplayer?!
6. Potential for character customisation and possible progress.
Just think, kiddies, this could be the next Unreal Tournament (It won't be, but that'd be cool). A multiplayer with a story, a degree of character choice (Unreal Tournament was quite varied, IMHO) and variety of weaponry. I would also guess that it's going to be a bit like other FPS games in that there'll be classes to choose from.
If this is real, then I think they should go for a TPS rather than an FPS. The market is flooded with FPS games with multiplayer capabilities, but if they take a lead out of Valve and (Early) Epic's book (i.e. the multiplayer being a separate product to the single player), we could see a good product being released. As it's possibly a BioWare Montreal production (I think that's what has been said, at least), it won't impact on Mass Effect 3 (As it's a BioWare Edmonton game).
Ah, I'm gonna have fun deciding what I'd like to see.