Packs can be quite large. Even with current system, sometimes many nephs spawn at once. Rare traits, well, they are rare. Even with constant flow of new nephs, it can be extremely hard to get what you want (wasted like two hours trying to get slim trait), just some rebalancing needed. I don't see current system of traits staying as it is, endless breeding to get specific trait is tedious and messy (you can have only so much pairs before inbreeding trait gets you).
Good system would be something like bees, from modded minecraft, where you extract genomes to mod next generations. Not as complex though. BotN already uses "genomes" in forms of liquids, Helmsman can use it easily. Even by just adding new chemist NPC that sells mods with higher chance of specific mutations in exchange for specific set of liquids and money. Even though I'd personally prefer more gamey systems with RnD tech and more sexy interactions with nephs, like sex/endurance training and automation, so far game is not fun after like an hour, even Cloud Meadow is much more content packed and thought through.
And no, highpoly. Even on potato PC didn't notice much difference between furry and skinny. For me biggest performance hit were animations for some reason. It may be due to fur, maybe more of it loads in for anims, but even non furry nephs tanked performance when animation starts. And sometimes it legit looks like every frame of animation new model loads in, or maybe it's my sight getting worse due to too much lewd games.