^ Which is one of the reasons a prequel is the most likely choice. If you think about it, the real untold story of Mass Effect is the one they tried to tell in the novelizations: the adventures of John Grissom and David Anderson, the discovery of the Charon Relay, the First Contact War and the occupation of Shanxi, etc. We sometimes forget that those events totally reshaped the way humanity viewed itself and the universe around them... and they happened less than a generation before Mass Effect 1.
You could spend AT LEAST one game exploring those first steps into space, depending on where you started. I could see Bioware letting you start the game as a Privateer, a Merchant, a Mercenary or an Explorer; your opening missions, the kind of ship you're flying and the kind of equipment you can take with you depend entirely on your choice, even if the game ultimately ends with the Council stepping in and telling the Turians to calm the fuck down. I'd also be looking forward to seeing the Batarians actually show up as a primary adversary instead of a bunch of four-eyed canonfodders who don't know any better.
I just realized this, too: in all of Mass Effect, we never did get to see what a Batarian warship looked like, did we?