I don't think Kartik - Naina would happen. Kartik seems to have interested eyes only for Sunaina. Though he has other girls in his gang, his behaviour towards Sunaina is different (like getting chocolates for her, and not for the other girls in his group).
Also the spoiler which was seen where Kartik stares at Naina, but it wasn't shown in the show.
I feel though Kartik is a spoilt brat, he seems to be decent when behaving with girls. I have never felt him eyeing any girl wrongly, even Naina, Swati or Preeti inspite of his tashan with Sameer.