Interesting. A MMO set in the Mass Effect universe would actually work, and that would actually be amazing. Think Star Wars galaxy's but bigger, better and with Mass Effect epicness.
wait.. old republic isnt even out yet and they're talking about a mass effect mmo? not even blizzard attempted to have two mmo's at the same time. mass effect mmo would work as a guild wars style "mmo." the city would be like a lobby (everyone sees each other, can chat with each other) and when you go out into the world, it's only you and your party/raid.
How about just starting with allowing another player online to control other members of your party in future Mass Effect games? It can still be just as much of a single player game that way. It worked (extremely well, BTW) in Secret of Mana all those years ago on the SNES (but obviously offline).
It was too mellow. Take away the great single player story and their is no reason to play it. It's would be like a Heavy Rain MMO.
I would play a Mass Effect MMO. I love the Mass Effect universe, and think this could be just as epic as WoW if done right. Although things must not be going too well with the development of their Star Wars MMO if they're already contemplating this. The word of mouth on it hasn't been too good. The problem with MMOs in general is that they need to have a huge following to be worthwhile. Everquest and WoW are the only two that have been successful. Most have flopped.