I'll refrain from commenting on ToR since while I play it my reactions are mixed. I've already said everything I feel I need to say on the subject in other threads.
I find nothing inherantly wrong with the idea of an MMO set in the Mass Effect universe, but to be honest I think it would be a retread of ToR. Mass Effect was the spiritual successor to the single player KoToR games and even touted as such, and it hits a lot of the same tropes as Star Wars as a matter of design.
In the end it would be another ground based sci-fi RPG, and really I don't think we need another one of those right now. Really I'm likely to only be interested in another sci-fi MMO if it launches with both a decent space and ground based component. Star Trek Online tried that with mixed results, as did SWG, and I don't think either did it wll. Create a full featured ground and space component together, like ToR on the ground and EVE in space and I might be interested.
I'll also say that I don't much care for the linear nature of MMOs nowadays, ToR in paticular feels pretty limited. To really sell me we're going to see the return of more open enviroments and choice of progression. Star Wars Galaxies (SWG) had it's problems, but in playing ToR I can't help but feel crowded and limited compared to what the previous Star Wars RPG managed to accomplish. I mean even now I walk past, see a cool looking creature and think "damn, if this was SWG I could ride one of those".
In short the Mass Effect liscence is okay, but they'd need more than that to sell me. They would need to produce a really amazing game around it, and one that isn't simply going to do the same thing as most other MMOs with differant thematic material. I'd kind of like to see another attempt at actual hardcore, open world, MMOing, rather than the trend that is leaning towards casual oriented, cinematic experiences. I mean ToR is fun, but in the end I have to say I probably got more enjoyment collecting and placing trophies from my adventures in my houses in SWG than I did listening to some guy gargle into a microphone while subtitles explain that the alien wants me to go click on 10 cages holding captured soldiers to free them. Quests like that are fine, and belong in the open world game too, but the point is that when I compare listening to a guy gargling into a mic, to say being able to eventually ride almost any creature I see in the world (or make it fight for me) or stake my own property in an open world and decorate my house... join player cities, and have players walk past them and see what we've set up... to me it just didn't turn out being a worthwhile trade off. I guess opinions vary though.
Allow me to fly a ship RPG style like in EVE between planets, and colonize planets and build houses/habitats on them, and I'll be interested in Mass Effect. If you just want me to run from quest to quest through very little paths, jump like mario from pipe to pipe to collect datacrons, and other things with voicework being the major selling point... I'll pass, largely because I already have ToR for that.
It's unlikely though because as a liscence Mass Effect involves no real interactive space combat, or colonization or anything. It's very much a focused military universe, and in all likely the essence of the series would be people developing special forces guys from various alien races and dropping onto planets to shoot stuff.
For those who read this far, I'd imagine Mass Effect Online would probably be "Tabula Rasa 2" when you get down to it. It's a matter of opinion whether that's good or not, speaking for myself, Tabula Rasa didn't hold my attention very long.