Mass Effect is not Knights of the old republic. Kotor was made as a standalone game whose sales made lucasarts interested in a sequel. That sequel ended up being made by a completely different company that decide to start over with a clean slate so theyd be free to do what they wanted. ME2 is a seuqel planned from the beginning and made by the exact same people who made the first game, and its been in production since before ME was released. For them to introduce a new main character at this point would completely break the cohesion of the trilogy.
Ah freck.... why am I even writing this, OF COURSE bioware are just teasing us. Its so blatantly obivous that its not even worth discussing.
I should add sarcasm tags next time.