I completely agree with you. NK is one of my favourite character's on the show. He's fresh and she bring so much to the show. I absolutely LOVE his and Khushi's relationship. I love their friendship. It's so pure. They genuinely care for each other. Besides the obvious, this is one of the best relation the show has brought forth. I mean I love Arnav's and Anjali's relationship and even aakash and arnav but none of them (in my opinion) are as good as khushi and NK's relationship.
I really want the production house to keep Karan on as a fulltime cast member. I know that they can probably do a lot with his character. I don't want him to just walk in khushi's shadow but I want him to also develop as a character. Perhaps the writers can involve khushi in his character development but there's a lot we really don't mow about him and it would be nice if the writers explored that.
Anyways I hope the production house knows what a valuable asset Karan (and his character of NK) is to the cast and the show and they keep him on forever.