OK, here's the long-shot hope for, but...
I am hoping Liara is the star of the Mass Effect 2 expansion. In short, I want to see an "Awakening" style expansion for ME2 that ditches Shepard for a while, picking up Liara as the new main character.
There's a whole host of reasons this would be awesome.
1. It lets the Shepard plot rejig for the finale. With a nice breather story arc in place, the story can be smoothed into place for the best setup into the last chapter of the trilogy.
2. It allows Bioware to resolve a subplot without it dominating the third game.. C'mon. The fate of the Shadow Broker turned into a loyalty mission? Get real. The Shadow Broker's demise is a plot that requires about twenty hours to resolve, surely. It's a perfect story for an expansion.
3. It uses a familiar face distanced from the main storyline, uniquely suited to the game's mechanics. With Liara's distancing from Shepard, she can now set up her own plot that can impact upon while not distracting from his/her main story. In addition, her personality shift from game 1 to 2 neatly puts her in the crux of Paragon/Renegade. Do you play her as the naive, caring scientist of game 1? (Paragon) Or do you further her shift to cold-hearted pragmatist in game 2? (Renegade.)
There's also some really good reasons why it won't happen.
1. No character customisation. Bioware always does character customisation. Liara's face and look, however, is set. It would be jarring to not have the options to make your own character.
2. Set powers She's a biotic. It's what she does. You could not play it as a tech specialist or fighter.
3. Just plain seems unlikely. Bioware seem pretty determined to follow Shepard. Much as I love the main-character with minor-character chapter intermissions model (which the original Half-Life did so well) it doesn't feel like Bioware's MO.
(ps. Oh, and my pick? The Shadow Broker is an AI. Thus it can be destroyed, but it's no small task.)