I have no idea. When zain was in tashan e ishq, and there was the track where the female lead (twinkle played by jasmin bhasin) was discovered to have a younger sister, and she was going to be cast opposite zain's character yuvi, I suggested hiba nawab would look good as jasmin's younger sister role, and would look good with zain. But currently she is doing a comedy show, and now that I think about it, Hiba seems to have become incredibly annoying over the years. Something about her babyish and over-hyper behaviour puts me off her, and I think she would annoy the hell out of zain, rather than him finding her cute, but a lot of her co-stars speak very positively about her and call her cute and really sweet, but acting wise I find her super average, whereas zain I think is really improving from his tashan e ishq days. So I would give hiba a pass for now.
I wouldn't mind seeing him opposite additi gupta, although for some reason she doesn't seem to do positive lead roles nowadays since her very first show with ekta, kis desh mein hain mera dil. Now she does negative lead roles. Not sure why she doesn't seem to take up positive ;ead roles, but she is a good actress, and loved her as evil sanam in qubool hai.
I wouldn't be sure about them casting him with a fresh face, because I would want him to work with an experienced actress, but I'm not sure who else I would like to see opposite him.