Hey, seeing as you liked my tweet on marble foxes earlier, I thought I'd make a few additional small suggestions on here! Since Twitter is very restrictive on typing, haha.
-You said you want to implement simple genetics-- which is a really interesting point, since marble foxes are actually a mutation that results from breeding captive red foxes! Not sure exactly how it works, but it must be similar to the differences in wolves and domestic dogs lol. Perhaps there could be a domestication system at some point-- wild animals would spawn with certain traits, and breeding them has a chance of new traits appearing, etc. I'm not sure how "simple" that is, but it'd be cool! For example, you said you wanted to add working dogs-- you could have standard wolves have, say, normal ears, but if you breed them enough you might start seeing floppy ears or different coloring, etc. Just a thought-- I'm very curious to see how you'd implement genetics btw, not many mods do that and it's something that's always interested me!
As an aside, this site has some interesting fox color morphs if you're looking for inspiration http://livingwithfoxes.weebly.com/colour-morphs-of-hybrid-foxes.html
-Also please more ferret stuff because ferrets are so underrated and oh my goodness yes <3
Anyway, just a few thoughts on foxes/marble foxes! Thank you for your time!