I still think it's likely that this emotional scene Ian was talking about was a flashback to a first meeting with Elena we aren't aware of....
If the YT spoilers do happen, then I want an emotional goodbye scene. Perhaps Damon could tell Elena that he'd met her before as he's saying goodbye....I'll repost my theory
In terms of Damon and Elena's first meeting, I would love it if Damon and Elena had had some kind of interaction even almost romantic meeting. Perhaps Damon had approached her as if she was Katherine. Maybe kissed her or professed his love to her? Elena being the empathetic person she is tries to reason with Damon and feels sorry for him. Damon in talking to her comes to the realisation she isn't Katherine, and connects with her in some way. No matter how brief. The way I see it is like that moment in the kitchen, when Damon lets his guard down a bit when someone finally is showing him genuine kindness and sympathy. However being in the state he was at the time, these moments pass very quickly as he refuses to let that humanity in. He compells Elena to forget his moment of weakness and pledges to use her in his mind games against Stefan, unaware he will fall in love with her as he is still very much in love with Katherine at this time.
It would be a really beautiful moment if Elena is confiding in Damon how she is terrified of becoming like Katherine, and that she hates what she's doing to Damon and Stefan. Damon can then comfort her by telling her about their first meeting, and how he realised she could never have been Katherine because of her pure heart and kindness. He could tell her that she was the first person to break through and touch his heart in years, and he knew in that moment she was nothing like Katherine. It would be really lovely that despite his inhumane state Damon managed to connect with Elena and it would show Elena how well he truly knows her and the inner beauty he recognised.....