I was hoping the LI would show up on the Citadel if she's a potential squad member. Shepards about to make his final choice, he knows he's going to die, but he won't die alone. His LI will be with him until the end. The choice is made, Shepard falls to the floor, exhausted, his LI beside him and they just sit together and look out as the galaxy is "saved."
Honestly I don't see why that couldn't have happened. If Anderson can show up, why not the LI? In all 3 games, the culmination of the romance has basically been the sex scene. In ME3 you do get another scene before the final assault at the FOB, but in the end, Shepard is alone. However the game ended, I think it would have been fitting for the person he cared for most to be with him in that final moment. Maybe they'd live happily ever after. Maybe they'd die. But at least they'd be together and not a galaxy apart.