I got your game when you released your latest video and I am in love. There is something profound that strikes me when I see the end of day long simulations. This game has been my obsession and the hours on my steam account show that. With that however I'd like to add a few things.
I'm not sure if you take suggestions or anything but it would certainly be neat to have more sandbox maps. Or alternatively different settings that help make the map more extreme. The temperature setting is a good way to encourage change.
However change across a species into very different ones can take a long time through mutations. I'm not sure how possible it would be but a map that has some form of a continental drift could help encourage mutations that drastically alter a species into several in a shorter amount of time. I see water level changes already with temperature so altering that to follow some sort of noise as well could work.
I also think aquatic life as animals and plants would rock, especially if they are able to transition onto land. I have no idea if this would be possible or how you would even begin to implement it.
This game is amazing and you should be immensely proud. I am so glad it is early access not because I think it needs more, but because I am excited to see it grow.
The Sapling is something I will come back to time and time again and is an absolute bargain for the price you are selling for. You could easily double the price and the quality of your work and the entertainment of your game would still be worth it.