So, the rumor mill is starting up about a supposed Damon/Katherine sex scene, and 99% of DE fans are FRAKIN OUT.
But personally, even if there is one, it's not going to be a big deal. Why you ask? Well, let's look at the facts.
There is the possibility that this scene would be a flashback, therefore-no need to worry there.

Then there is the possibility that it is in the present. Now, if you remember back in 3x05 when Damon and Katherine made out, Damon says, "You just don't do it for me anymore." and I really don't think the writers were just trying to throw us DE fans a bone here- I think that they meant it. And If you have read as to why, it says that Stefan and Elena have an...encounter, and Damon flips out after seeing it. Anger sex. Yes, extremely heartfelt and romantic. And if you look at most instances throughout the series with sexual interaction between Damon and Katherine, they have all just been meaningless flings. The only time he ever acted anywhere NEAR romantic towards her was in 1x22, was when he thought it was Elena.
Then of course there is other possiblities, maybe a fantasy or something to make Stefan mad and make him come to his senses. Who knows.
But what I am trying to say is, at the end of the day, I do believe if it turns out to be true, it will mean the same way as it always does between to two-nothing. Absolutley nothing. We all know that Damon is madly in love with Elena, and at this point in their relationship, even if he did, he will never love Katherine the way he does Elena.

Or, I could be doing this ranting for nothing, and we could have just been screwed with the whole time...who knows!