So ok, if the nipples are there on the females as an old pheromone distributor (if that is indeed the new reason, and no longer to dispense kwell), then they were there for a sexualized reason.
Not necessarily in the way humans are attracted to nipples, but in a sexual realm nonetheless. They attracted a mate for sex. THAT'S FINE. Be a man, Sam. Just own what you love rather than because weird about it. Half of this shitting on by Kiwi and fans is because you give fucking asinine reasons for your obvious fetishes. People are less likely to dogpile on someone with integrity for their art. Again, I said it before, fetishes are fine when exposed to the right audience and you actually own them.
Also, the appendix analogy actually kind of hurts Sam's vision of these aliens being...well, alien. Rainy does him no favours with this.
Our human evolution for not being able to deal with useless organs and appendages should not be made for a comparison for a supposed hyper-evolved ancient race. Yes, insects have vestigial organs too, but that's because our planet and life is young. If the Kiv predate the universe and indeed live for millions/billions of years, shapeshift (based on older footage, not sure if still canon), and literally fight to be the strongest and genetically superior young (I do NOT mean that in a eugenics type of way BTW, I mean it purely survival of the fittest), why the hell would the choose to have nipples if not to keep them for sexual reason?
Use insects as a base idea of how to model your aliens, but try to think outside the box on how evolution works. Especially for a world that works in what seems to be 4th dimensional.
I dunno. Maybe this is just a rant to the void. If Sam and Rain do read this, it's not meant to come off as mean; it's a purely constructive critique into your world and perhaps something to think about. I stopped actively being in Fennah's community a few years back now, but I still want him to succeed.