Quoting Yarlen, reply 1There are no plans to ever release a non-Steam version of Sins: Rebellion.
Wait, WHAT?!, I remember you guys talking about bringing SDC back? What the hell! I was waiting for it, I've sent you PMs about it.
They are bring back SDC, but Rebellion is a steamworks game, so it doesn't matter how they distribute it, in the end you must always use steam.
I think the plan is that for versions of Sins before Rebellion, you will be able to use SDC instead of Impulse.