TBH, I don't mind them cutting a few bits out for DLC, providing that they expand on it, which is what the Omega DLC sounds like.
The Citadel DLC - I'm still not sure on this. The most obvious plot would be that you play someone like Bailey during the Cerberus/Reaper invasion at the end of the game. However, with one small exception aside (Joker in ME2), you've ALWAYS played as Shepard.
I just hope that all of the remaining DLC isn't just mid-game content. Citadel DLC would fill an obvious POV gap from the main game, plus might impact and/or overflow with the ending(s).