@Maisu - Think of it serial wise, you had this huge , huge build up with Harshad twice already. Musicana night and then this jail-time, How can a show being him back and strking the same blows when there has not been some space or normlacy.
I don;t think he is a factor to Manik-Nandu equation at all. His main conflict is with Manik on two points -Noyonika and that night. If they go with the former , it will mean bringing Noyonika to the fold, which again means she will factor only in Manik-Nandini track , the rest of fab4 will not have much affect of her presence , because they have been always around. Nandini will different for Noyonika to deal with.
I don't think career is a good conflict right now. Nandu is 17 , she has a music degree to finish and it's too early for her to go through this right now. Could be a factor only when everything is fine, Manik is a big rockstar and then the issue of her identity can be played. But honestly that will be stretching their target audience.
These two are sold on the premise that they get each other, communicate so any other internal issue won't make sense as a conflict. let the secrets come out and overwhelm them , that is the next struggle for them, to save their love and fight against the odds.
And if they go about the band of brothers, then first they need Dhruv breaking down and his disease revisited.
If Harshad has to common back after Soha , he will have to target someone else other than Manik to keep the repetitive drag away.