They would have an utterly boring chemistry, seriously, like I said before watch their previous scenes together, zilch., n whats more, what could you possibly gain from the matchup, it would negate from the fact that saras loves kumud, and to a lesser extent kusums own love for her sister. I mean everything has been done, there would be not much to work with, I'm shocked that a sister would put her sister through this, it is selfish, kusum has her own life to live and contrary to the anti kusum people I don't think she likes saras, its a horrible thought, I'd she did it would prove she is heartless and doesn't truly care for her didi, which as it stands she seems quite close to.
Also if anything does happen on that front it will probably be right at the very end, because it would be the end of the samud affair, both of them married to other people. So samud lovers have to stop whining about that as nothing will happen until the dying moments of the show if it does follow from the original story, and similarly the lovers of this post need to wake from their fantasies because its highly unlikely that you will get a new love story with saras for someone different to kumud. Kusum ain't no kumud, kusum is kusum as her daddy told her.
Atleast with Sunny there is a better chance for 2 sided love and not another tragedy. Without anything significant happening yet between them, Sunny actually has chemistry with Kusum, they just need the opportunity and contexts for the viewers to realise their potential as a pair.