Hey! Feels weird making this my first post, but I used to be one of the super early beta testers from the facebook days. I've still been playing from time-to-time so here are some suggestions partially based on the older demos:
The first version I played was before you guys introduced the island idea. It was one giant land mass with hot edges and a temperate center. It would be neat if the next game took a que from dwarf fortress or rimworld and let us choose a "site" on a much larger continent to live on, with the ability to adjust how big the gameplay area is. The main difference between this idea and the islands is that it allows more biome diversity, since there wouldn't always be an ocean on the edge of the map, and those biomes can be significantly larger so if a player decides to move their tribe across the continent it wouldn't always be a (relatively) quick hop to the other side of a harsh environment.
Depending on what you guys plan to do, settings options to choose between being on a continent vs island might work. Alternatively, you could improve how dwarf fortress' "site" system works and allow players to move the playable area similarly to how the islands work now, by moving all of the ones your plan to take to the edges of their "territory" before the players push to move in that direction. The "site" would then move a square over on the world map, and allow larger tribes to stick together instead of picking a handful who can move on.
I think this system would also allow weather and seasons to provide some impact to gameplay. In the original, it didn't make too much sense to add difficult weather outside of certain islands to help differentiate them. With a global map and "site" system, players might be in a single biome for a rather long time, so adapting your species to the weather in that area as well as the climate would add to the gameplay. Along with the weather acting as a signal that you should adapt your species before you keep going forward.
For example, if your temperate-aligned animals are moving north, the rains get colder. The area would normally be warm but the cold rains signal that your species needs to adapt before they hit an icy region. Cold rains can also be a signal that winters here get much colder than your animals can handle, even if they can live in the area during summer, and it would be a good idea to move back down south before it gets too cold.
Next idea comes from one of the facebook beta builds: Age-related traits. At the time you guys had the nichelings' fur get darker with age, it was removed in later builds. I think that should be brought back if you plan to expand the genetics system, it would be neat to have different genes affect aging. Different white or black fur patterns that show for age-related reasons, and animals losing strength and speed after reaching their elder years, would be neat to see.
Now here are ideas I've had over the years from playing the finished product:
Let adults pick up babies. The main reason I've personally never had an entirely sneak and speed-based species is that if I build a nest and a carnivorous animal shows up the next turn, I can not move the mom. The baby will be eaten. Admittedly, feeding your babies to carnivorous animals is a strategy some animals use, but most of the ones that have children who can't immediately walk will try to pick one up as they're running away.
In-Depth family trees. I'm not sure how viable this is for you guys so it's not a huge deal, but there is a little open-source project called Clangen with a neat family tree system. The main reason it works, I think, is because of the afterlife menu that allows you to keep cats around or let them fade. Fading allows their details to be deleted by the game and leave little ghost image in their place that lets you know "someone existed there", and how long it takes for them to fade can be customized. You can't, for instance, click on the little ghost image to see if they had descendants, you can only mouse over and see their name. For Niche 2, I probably wouldn't call it an afterlife, but having a similarly styled menu off to the side as an "archive" or "graveyard" would allow people to scroll through their family tree, should the player choose to make sure that specific animal's details don't fade. Fading would also prevent the Crusader Kings 2 problem where the family tree will lag horrifically after enough generations pass. Clangen also allows renaming the not-faded dead and adding biographies, which is neat for players who like to tell stories that involve current generations changing details from the past or mythologizing their ancestors. That last part really isn't necessary for this kind of game but it's something to consider.
Auto-resource gathering. Clicking on every individual animal to get food and straw is a bigger population cap than the resources themselves and part of why I never return to old saves anymore. I like playing with big tribes but I can't remember what all 50+ of them were supposed to be doing when I get back. On paper, it's not a big deal to roll with it, but it also slows things down so much that it turns into death by 1000 cuts.
Sex-linked genes. I'm specifically referring to the mane. Sometimes I just want the mane to not be sex-linked. At the same time, sometimes I want other traits to be sex-linked. Genetically, I have no idea how traits develop sex linkage or how it's possible for them to stop being sex-linked, but since the original game does allow us to mutate gills and webbed feet onto a baby whose parents were both bear hybrids with no family history of either of those traits, I'm not sure how hung up on accuracy we need to be for making traits sex-linked or removing the sex-linkage from other traits.
Give birth without a nest. It should be dangerous, harmful to the mother, and potentially result in a stillbirth; but I'd vastly prefer the risk of losing the baby to the eternal pregnancy thing we have in the original. Especially when part of the challenge was supposed to come from having rogues around trying to sneak-breed your females. Why would I ever have the ones I want to breed move around before they're pregnant by the creatures in my tribe? Why would I let a creature I never planned to breed take up the limited space and resources on a nest just to have a baby I'll likely throw into the ocean? Admittedly they only go into the ocean if they're eternally sick, but the point stands. It's honestly something I've always been annoyed about but tolerated because it was the first type of game going into this kind of depth. I really, really don't want to see eternal pregnancies in the second game.
Others have already brought up splitting the tribe so they have their own resources and allowing creatures who aren't part of your tribe(s) to reproduce on their own, so I won't rehash that, I'm just putting this here to let it be known I've also had that idea for a while and would like to see them as well.
